Merge tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU changes from Ingo Molnar:

 - Debugging for smp_call_function()

 - RT raw/non-raw lock ordering fixes

 - Strict grace periods for KASAN

 - New smp_call_function() torture test

 - Torture-test updates

 - Documentation updates

 - Miscellaneous fixes

[ This doesn't actually pull the tag - I've dropped the last merge from
  the RCU branch due to questions about the series.   - Linus ]

* tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (77 commits)
  smp: Make symbol 'csd_bug_count' static
  kernel/smp: Provide CSD lock timeout diagnostics
  smp: Add source and destination CPUs to __call_single_data
  rcu: Shrink each possible cpu krcp
  rcu/segcblist: Prevent useless GP start if no CBs to accelerate
  torture: Add gdb support
  rcutorture: Allow pointer leaks to test diagnostic code
  rcutorture: Hoist OOM registry up one level
  refperf: Avoid null pointer dereference when buf fails to allocate
  rcutorture: Properly synchronize with OOM notifier
  rcutorture: Properly set rcu_fwds for OOM handling
  torture: Add kvm.sh --help and update help message
  rcutorture: Add CONFIG_PROVE_RCU_LIST to TREE05
  torture: Update initrd documentation
  rcutorture: Replace HTTP links with HTTPS ones
  locktorture: Make function torture_percpu_rwsem_init() static
  torture: document --allcpus argument added to the kvm.sh script
  rcutorture: Output number of elapsed grace periods
  rcutorture: Remove KCSAN stubs
  rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp()
  ...

Documentation/RCU/Design/Data-Structures/Data-Structures.rst

@@ -963,7 +963,7 @@ exit and perhaps also vice versa. Therefore, whenever the
 ``->dynticks_nesting`` field is incremented up from zero, the
 ``->dynticks_nmi_nesting`` field is set to a large positive number, and
 whenever the ``->dynticks_nesting`` field is decremented down to zero,
-the the ``->dynticks_nmi_nesting`` field is set to zero. Assuming that
+the ``->dynticks_nmi_nesting`` field is set to zero. Assuming that
 the number of misnested interrupts is not sufficient to overflow the
 counter, this approach corrects the ``->dynticks_nmi_nesting`` field
 every time the corresponding CPU enters the idle loop from process

Documentation/RCU/Design/Requirements/Requirements.rst

@@ -2162,7 +2162,7 @@ scheduling-clock interrupt be enabled when RCU needs it to be:
    this sort of thing.
 #. If a CPU is in a portion of the kernel that is absolutely positively
    no-joking guaranteed to never execute any RCU read-side critical
-   sections, and RCU believes this CPU to to be idle, no problem. This
+   sections, and RCU believes this CPU to be idle, no problem. This
    sort of thing is used by some architectures for light-weight
    exception handlers, which can then avoid the overhead of
    ``rcu_irq_enter()`` and ``rcu_irq_exit()`` at exception entry and
@@ -2431,7 +2431,7 @@ However, there are legitimate preemptible-RCU implementations that do
 not have this property, given that any point in the code outside of an
 RCU read-side critical section can be a quiescent state. Therefore,
 *RCU-sched* was created, which follows “classic” RCU in that an
-RCU-sched grace period waits for for pre-existing interrupt and NMI
+RCU-sched grace period waits for pre-existing interrupt and NMI
 handlers. In kernels built with ``CONFIG_PREEMPT=n``, the RCU and
 RCU-sched APIs have identical implementations, while kernels built with
 ``CONFIG_PREEMPT=y`` provide a separate implementation for each.

Documentation/RCU/whatisRCU.rst

@@ -360,7 +360,7 @@ order to amortize their overhead over many uses of the corresponding APIs.
 
 There are at least three flavors of RCU usage in the Linux kernel. The diagram
 above shows the most common one. On the updater side, the rcu_assign_pointer(),
-sychronize_rcu() and call_rcu() primitives used are the same for all three
+synchronize_rcu() and call_rcu() primitives used are the same for all three
 flavors. However for protection (on the reader side), the primitives used vary
 depending on the flavor:
 

Documentation/admin-guide/kernel-parameters.txt

@@ -3095,6 +3095,10 @@
 			and gids from such clients.  This is intended to ease
 			migration from NFSv2/v3.
 
+	nmi_backtrace.backtrace_idle [KNL]
+			Dump stacks even of idle CPUs in response to an
+			NMI stack-backtrace request.
+
 	nmi_debug=	[KNL,SH] Specify one or more actions to take
 			when a NMI is triggered.
 			Format: [state][,regs][,debounce][,die]
@@ -4174,46 +4178,55 @@
 			This wake_up() will be accompanied by a
 			WARN_ONCE() splat and an ftrace_dump().
 
+	rcutree.rcu_unlock_delay= [KNL]
+			In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
+			this specifies an rcu_read_unlock()-time delay
+			in microseconds.  This defaults to zero.
+			Larger delays increase the probability of
+			catching RCU pointer leaks, that is, buggy use
+			of RCU-protected pointers after the relevant
+			rcu_read_unlock() has completed.
+
 	rcutree.sysrq_rcu= [KNL]
 			Commandeer a sysrq key to dump out Tree RCU's
 			rcu_node tree with an eye towards determining
 			why a new grace period has not yet started.
 
-	rcuperf.gp_async= [KNL]
+	rcuscale.gp_async= [KNL]
 			Measure performance of asynchronous
 			grace-period primitives such as call_rcu().
 
-	rcuperf.gp_async_max= [KNL]
+	rcuscale.gp_async_max= [KNL]
 			Specify the maximum number of outstanding
 			callbacks per writer thread.  When a writer
 			thread exceeds this limit, it invokes the
 			corresponding flavor of rcu_barrier() to allow
 			previously posted callbacks to drain.
 
-	rcuperf.gp_exp= [KNL]
+	rcuscale.gp_exp= [KNL]
 			Measure performance of expedited synchronous
 			grace-period primitives.
 
-	rcuperf.holdoff= [KNL]
+	rcuscale.holdoff= [KNL]
 			Set test-start holdoff period.  The purpose of
 			this parameter is to delay the start of the
 			test until boot completes in order to avoid
 			interference.
 
-	rcuperf.kfree_rcu_test= [KNL]
+	rcuscale.kfree_rcu_test= [KNL]
 			Set to measure performance of kfree_rcu() flooding.
 
-	rcuperf.kfree_nthreads= [KNL]
+	rcuscale.kfree_nthreads= [KNL]
 			The number of threads running loops of kfree_rcu().
 
-	rcuperf.kfree_alloc_num= [KNL]
+	rcuscale.kfree_alloc_num= [KNL]
 			Number of allocations and frees done in an iteration.
 
-	rcuperf.kfree_loops= [KNL]
-			Number of loops doing rcuperf.kfree_alloc_num number
+	rcuscale.kfree_loops= [KNL]
+			Number of loops doing rcuscale.kfree_alloc_num number
 			of allocations and frees.
 
-	rcuperf.nreaders= [KNL]
+	rcuscale.nreaders= [KNL]
 			Set number of RCU readers.  The value -1 selects
 			N, where N is the number of CPUs.  A value
 			"n" less than -1 selects N-n+1, where N is again
@@ -4222,23 +4235,23 @@
 			A value of "n" less than or equal to -N selects
 			a single reader.
 
-	rcuperf.nwriters= [KNL]
+	rcuscale.nwriters= [KNL]
 			Set number of RCU writers.  The values operate
-			the same as for rcuperf.nreaders.
+			the same as for rcuscale.nreaders.
 			N, where N is the number of CPUs
 
-	rcuperf.perf_type= [KNL]
+	rcuscale.perf_type= [KNL]
 			Specify the RCU implementation to test.
 
-	rcuperf.shutdown= [KNL]
+	rcuscale.shutdown= [KNL]
 			Shut the system down after performance tests
 			complete.  This is useful for hands-off automated
 			testing.
 
-	rcuperf.verbose= [KNL]
+	rcuscale.verbose= [KNL]
 			Enable additional printk() statements.
 
-	rcuperf.writer_holdoff= [KNL]
+	rcuscale.writer_holdoff= [KNL]
 			Write-side holdoff between grace periods,
 			in microseconds.  The default of zero says
 			no holdoff.
@@ -4291,6 +4304,18 @@
 			are zero, rcutorture acts as if is interpreted
 			they are all non-zero.
 
+	rcutorture.irqreader= [KNL]
+			Run RCU readers from irq handlers, or, more
+			accurately, from a timer handler.  Not all RCU
+			flavors take kindly to this sort of thing.
+
+	rcutorture.leakpointer= [KNL]
+			Leak an RCU-protected pointer out of the reader.
+			This can of course result in splats, and is
+			intended to test the ability of things like
+			CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
+			such leaks.
+
 	rcutorture.n_barrier_cbs= [KNL]
 			Set callbacks/threads for rcu_barrier() testing.
 
@@ -4512,8 +4537,8 @@
 	refscale.shutdown= [KNL]
 			Shut down the system at the end of the performance
 			test.  This defaults to 1 (shut it down) when
-			rcuperf is built into the kernel and to 0 (leave
-			it running) when rcuperf is built as a module.
+			refscale is built into the kernel and to 0 (leave
+			it running) when refscale is built as a module.
 
 	refscale.verbose= [KNL]
 			Enable additional printk() statements.
@@ -4659,6 +4684,98 @@
 			Format: integer between 0 and 10
 			Default is 0.
 
+	scftorture.holdoff= [KNL]
+			Number of seconds to hold off before starting
+			test.  Defaults to zero for module insertion and
+			to 10 seconds for built-in smp_call_function()
+			tests.
+
+	scftorture.longwait= [KNL]
+			Request ridiculously long waits randomly selected
+			up to the chosen limit in seconds.  Zero (the
+			default) disables this feature.  Please note
+			that requesting even small non-zero numbers of
+			seconds can result in RCU CPU stall warnings,
+			softlockup complaints, and so on.
+
+	scftorture.nthreads= [KNL]
+			Number of kthreads to spawn to invoke the
+			smp_call_function() family of functions.
+			The default of -1 specifies a number of kthreads
+			equal to the number of CPUs.
+
+	scftorture.onoff_holdoff= [KNL]
+			Number seconds to wait after the start of the
+			test before initiating CPU-hotplug operations.
+
+	scftorture.onoff_interval= [KNL]
+			Number seconds to wait between successive
+			CPU-hotplug operations.  Specifying zero (which
+			is the default) disables CPU-hotplug operations.
+
+	scftorture.shutdown_secs= [KNL]
+			The number of seconds following the start of the
+			test after which to shut down the system.  The
+			default of zero avoids shutting down the system.
+			Non-zero values are useful for automated tests.
+
+	scftorture.stat_interval= [KNL]
+			The number of seconds between outputting the
+			current test statistics to the console.  A value
+			of zero disables statistics output.
+
+	scftorture.stutter_cpus= [KNL]
+			The number of jiffies to wait between each change
+			to the set of CPUs under test.
+
+	scftorture.use_cpus_read_lock= [KNL]
+			Use use_cpus_read_lock() instead of the default
+			preempt_disable() to disable CPU hotplug
+			while invoking one of the smp_call_function*()
+			functions.
+
+	scftorture.verbose= [KNL]
+			Enable additional printk() statements.
+
+	scftorture.weight_single= [KNL]
+			The probability weighting to use for the
+			smp_call_function_single() function with a zero
+			"wait" parameter.  A value of -1 selects the
+			default if all other weights are -1.  However,
+			if at least one weight has some other value, a
+			value of -1 will instead select a weight of zero.
+
+	scftorture.weight_single_wait= [KNL]
+			The probability weighting to use for the
+			smp_call_function_single() function with a
+			non-zero "wait" parameter.  See weight_single.
+
+	scftorture.weight_many= [KNL]
+			The probability weighting to use for the
+			smp_call_function_many() function with a zero
+			"wait" parameter.  See weight_single.
+			Note well that setting a high probability for
+			this weighting can place serious IPI load
+			on the system.
+
+	scftorture.weight_many_wait= [KNL]
+			The probability weighting to use for the
+			smp_call_function_many() function with a
+			non-zero "wait" parameter.  See weight_single
+			and weight_many.
+
+	scftorture.weight_all= [KNL]
+			The probability weighting to use for the
+			smp_call_function_all() function with a zero
+			"wait" parameter.  See weight_single and
+			weight_many.
+
+	scftorture.weight_all_wait= [KNL]
+			The probability weighting to use for the
+			smp_call_function_all() function with a
+			non-zero "wait" parameter.  See weight_single
+			and weight_many.
+
 	skew_tick=	[KNL] Offset the periodic timer tick per cpu to mitigate
 			xtime_lock contention on larger systems, and/or RCU lock
 			contention on all systems with CONFIG_MAXSMP set.

MAINTAINERS

@@ -17672,8 +17672,9 @@ S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev
 F:	Documentation/RCU/torture.rst
 F:	kernel/locking/locktorture.c
-F:	kernel/rcu/rcuperf.c
+F:	kernel/rcu/rcuscale.c
 F:	kernel/rcu/rcutorture.c
+F:	kernel/rcu/refscale.c
 F:	kernel/torture.c
 
 TOSHIBA ACPI EXTRAS DRIVER

arch/x86/kvm/mmu/page_track.c

@@ -229,7 +229,8 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
 		return;
 
 	idx = srcu_read_lock(&head->track_srcu);
-	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
+	hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
+				srcu_read_lock_held(&head->track_srcu))
 		if (n->track_write)
 			n->track_write(vcpu, gpa, new, bytes, n);
 	srcu_read_unlock(&head->track_srcu, idx);
@@ -254,7 +255,8 @@ void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
 		return;
 
 	idx = srcu_read_lock(&head->track_srcu);
-	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
+	hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
+				srcu_read_lock_held(&head->track_srcu))
 		if (n->track_flush_slot)
 			n->track_flush_slot(kvm, slot, n);
 	srcu_read_unlock(&head->track_srcu, idx);

include/linux/rculist.h

@@ -63,9 +63,17 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
 	RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(),		\
 			 "RCU-list traversed in non-reader section!");	\
 	})
+
+#define __list_check_srcu(cond)					 \
+	({								 \
+	RCU_LOCKDEP_WARN(!(cond),					 \
+		"RCU-list traversed without holding the required lock!");\
+	})
 #else
 #define __list_check_rcu(dummy, cond, extra...)				\
 	({ check_arg_count_one(extra); })
+
+#define __list_check_srcu(cond) ({ })
 #endif
 
 /*
@@ -385,6 +393,25 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
 		&pos->member != (head);					\
 		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
+/**
+ * list_for_each_entry_srcu	-	iterate over rcu list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ * @cond:	lockdep expression for the lock required to traverse the list.
+ *
+ * This list-traversal primitive may safely run concurrently with
+ * the _rcu list-mutation primitives such as list_add_rcu()
+ * as long as the traversal is guarded by srcu_read_lock().
+ * The lockdep expression srcu_read_lock_held() can be passed as the
+ * cond argument from read side.
+ */
+#define list_for_each_entry_srcu(pos, head, member, cond)		\
+	for (__list_check_srcu(cond),					\
+	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
+		&pos->member != (head);					\
+		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
+
 /**
  * list_entry_lockless - get the struct for this entry
  * @ptr:        the &struct list_head pointer.
@@ -683,6 +710,27 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
 		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
 			&(pos)->member)), typeof(*(pos)), member))
 
+/**
+ * hlist_for_each_entry_srcu - iterate over rcu list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the hlist_node within the struct.
+ * @cond:	lockdep expression for the lock required to traverse the list.
+ *
+ * This list-traversal primitive may safely run concurrently with
+ * the _rcu list-mutation primitives such as hlist_add_head_rcu()
+ * as long as the traversal is guarded by srcu_read_lock().
+ * The lockdep expression srcu_read_lock_held() can be passed as the
+ * cond argument from read side.
+ */
+#define hlist_for_each_entry_srcu(pos, head, member, cond)		\
+	for (__list_check_srcu(cond),					\
+	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
+			typeof(*(pos)), member);			\
+		pos;							\
+		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
+			&(pos)->member)), typeof(*(pos)), member))
+
 /**
  * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
  * @pos:	the type * to use as a loop cursor.

include/linux/rcupdate.h

@@ -55,6 +55,12 @@ void __rcu_read_unlock(void);
 
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
+#ifdef CONFIG_TINY_RCU
+#define rcu_read_unlock_strict() do { } while (0)
+#else
+void rcu_read_unlock_strict(void);
+#endif
+
 static inline void __rcu_read_lock(void)
 {
 	preempt_disable();
@@ -63,6 +69,7 @@ static inline void __rcu_read_lock(void)
 static inline void __rcu_read_unlock(void)
 {
 	preempt_enable();
+	rcu_read_unlock_strict();
 }
 
 static inline int rcu_preempt_depth(void)
@@ -709,8 +716,8 @@ static inline void rcu_read_lock_bh(void)
 			 "rcu_read_lock_bh() used illegally while idle");
 }
 
-/*
- * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
+/**
+ * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
  *
  * See rcu_read_lock_bh() for more information.
  */
@@ -751,10 +758,10 @@ static inline notrace void rcu_read_lock_sched_notrace(void)
 	__acquire(RCU_SCHED);
 }
 
-/*
- * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
+/**
+ * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
  *
- * See rcu_read_lock_sched for more information.
+ * See rcu_read_lock_sched() for more information.
  */
 static inline void rcu_read_unlock_sched(void)
 {
@@ -945,7 +952,7 @@ static inline void rcu_head_init(struct rcu_head *rhp)
 }
 
 /**
- * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()?
+ * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
  * @rhp: The rcu_head structure to test.
  * @f: The function passed to call_rcu() along with @rhp.
  *

include/linux/rcutiny.h

@@ -103,7 +103,6 @@ static inline void rcu_scheduler_starting(void) { }
 static inline void rcu_end_inkernel_boot(void) { }
 static inline bool rcu_inkernel_boot_has_ended(void) { return true; }
 static inline bool rcu_is_watching(void) { return true; }
-static inline bool __rcu_is_watching(void) { return true; }
 static inline void rcu_momentary_dyntick_idle(void) { }
 static inline void kfree_rcu_scheduler_running(void) { }
 static inline bool rcu_gp_might_be_stalled(void) { return false; }

include/linux/rcutree.h

@@ -64,7 +64,6 @@ extern int rcu_scheduler_active __read_mostly;
 void rcu_end_inkernel_boot(void);
 bool rcu_inkernel_boot_has_ended(void);
 bool rcu_is_watching(void);
-bool __rcu_is_watching(void);
 #ifndef CONFIG_PREEMPTION
 void rcu_all_qs(void);
 #endif

include/linux/smp.h

@@ -26,6 +26,9 @@ struct __call_single_data {
 		struct {
 			struct llist_node llist;
 			unsigned int flags;
+#ifdef CONFIG_64BIT
+			u16 src, dst;
+#endif
 		};
 	};
 	smp_call_func_t func;

include/linux/smp_types.h

@@ -61,6 +61,9 @@ struct __call_single_node {
 		unsigned int	u_flags;
 		atomic_t	a_flags;
 	};
+#ifdef CONFIG_64BIT
+	u16 src, dst;
+#endif
 };
 
 #endif /* __LINUX_SMP_TYPES_H */

include/trace/events/rcu.h

@@ -74,17 +74,17 @@ TRACE_EVENT_RCU(rcu_grace_period,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gp_seq)
+		__field(long, gp_seq)
 		__field(const char *, gpevent)
 	),
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gp_seq = gp_seq;
+		__entry->gp_seq = (long)gp_seq;
 		__entry->gpevent = gpevent;
 	),
 
-	TP_printk("%s %lu %s",
+	TP_printk("%s %ld %s",
 		  __entry->rcuname, __entry->gp_seq, __entry->gpevent)
 );
 
@@ -114,8 +114,8 @@ TRACE_EVENT_RCU(rcu_future_grace_period,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gp_seq)
-		__field(unsigned long, gp_seq_req)
+		__field(long, gp_seq)
+		__field(long, gp_seq_req)
 		__field(u8, level)
 		__field(int, grplo)
 		__field(int, grphi)
@@ -124,16 +124,16 @@ TRACE_EVENT_RCU(rcu_future_grace_period,
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gp_seq = gp_seq;
-		__entry->gp_seq_req = gp_seq_req;
+		__entry->gp_seq = (long)gp_seq;
+		__entry->gp_seq_req = (long)gp_seq_req;
 		__entry->level = level;
 		__entry->grplo = grplo;
 		__entry->grphi = grphi;
 		__entry->gpevent = gpevent;
 	),
 
-	TP_printk("%s %lu %lu %u %d %d %s",
-		  __entry->rcuname, __entry->gp_seq, __entry->gp_seq_req, __entry->level,
+	TP_printk("%s %ld %ld %u %d %d %s",
+		  __entry->rcuname, (long)__entry->gp_seq, (long)__entry->gp_seq_req, __entry->level,
 		  __entry->grplo, __entry->grphi, __entry->gpevent)
 );
 
@@ -153,7 +153,7 @@ TRACE_EVENT_RCU(rcu_grace_period_init,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gp_seq)
+		__field(long, gp_seq)
 		__field(u8, level)
 		__field(int, grplo)
 		__field(int, grphi)
@@ -162,14 +162,14 @@ TRACE_EVENT_RCU(rcu_grace_period_init,
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gp_seq = gp_seq;
+		__entry->gp_seq = (long)gp_seq;
 		__entry->level = level;
 		__entry->grplo = grplo;
 		__entry->grphi = grphi;
 		__entry->qsmask = qsmask;
 	),
 
-	TP_printk("%s %lu %u %d %d %lx",
+	TP_printk("%s %ld %u %d %d %lx",
 		  __entry->rcuname, __entry->gp_seq, __entry->level,
 		  __entry->grplo, __entry->grphi, __entry->qsmask)
 );
@@ -197,17 +197,17 @@ TRACE_EVENT_RCU(rcu_exp_grace_period,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gpseq)
+		__field(long, gpseq)
 		__field(const char *, gpevent)
 	),
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gpseq = gpseq;
+		__entry->gpseq = (long)gpseq;
 		__entry->gpevent = gpevent;
 	),
 
-	TP_printk("%s %lu %s",
+	TP_printk("%s %ld %s",
 		  __entry->rcuname, __entry->gpseq, __entry->gpevent)
 );
 
@@ -316,17 +316,17 @@ TRACE_EVENT_RCU(rcu_preempt_task,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gp_seq)
+		__field(long, gp_seq)
 		__field(int, pid)
 	),
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gp_seq = gp_seq;
+		__entry->gp_seq = (long)gp_seq;
 		__entry->pid = pid;
 	),
 
-	TP_printk("%s %lu %d",
+	TP_printk("%s %ld %d",
 		  __entry->rcuname, __entry->gp_seq, __entry->pid)
 );
 
@@ -343,17 +343,17 @@ TRACE_EVENT_RCU(rcu_unlock_preempted_task,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gp_seq)
+		__field(long, gp_seq)
 		__field(int, pid)
 	),
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gp_seq = gp_seq;
+		__entry->gp_seq = (long)gp_seq;
 		__entry->pid = pid;
 	),
 
-	TP_printk("%s %lu %d", __entry->rcuname, __entry->gp_seq, __entry->pid)
+	TP_printk("%s %ld %d", __entry->rcuname, __entry->gp_seq, __entry->pid)
 );
 
 /*
@@ -374,7 +374,7 @@ TRACE_EVENT_RCU(rcu_quiescent_state_report,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gp_seq)
+		__field(long, gp_seq)
 		__field(unsigned long, mask)
 		__field(unsigned long, qsmask)
 		__field(u8, level)
@@ -385,7 +385,7 @@ TRACE_EVENT_RCU(rcu_quiescent_state_report,
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gp_seq = gp_seq;
+		__entry->gp_seq = (long)gp_seq;
 		__entry->mask = mask;
 		__entry->qsmask = qsmask;
 		__entry->level = level;
@@ -394,7 +394,7 @@ TRACE_EVENT_RCU(rcu_quiescent_state_report,
 		__entry->gp_tasks = gp_tasks;
 	),
 
-	TP_printk("%s %lu %lx>%lx %u %d %d %u",
+	TP_printk("%s %ld %lx>%lx %u %d %d %u",
 		  __entry->rcuname, __entry->gp_seq,
 		  __entry->mask, __entry->qsmask, __entry->level,
 		  __entry->grplo, __entry->grphi, __entry->gp_tasks)
@@ -415,19 +415,19 @@ TRACE_EVENT_RCU(rcu_fqs,
 
 	TP_STRUCT__entry(
 		__field(const char *, rcuname)
-		__field(unsigned long, gp_seq)
+		__field(long, gp_seq)
 		__field(int, cpu)
 		__field(const char *, qsevent)
 	),
 
 	TP_fast_assign(
 		__entry->rcuname = rcuname;
-		__entry->gp_seq = gp_seq;
+		__entry->gp_seq = (long)gp_seq;
 		__entry->cpu = cpu;
 		__entry->qsevent = qsevent;
 	),
 
-	TP_printk("%s %lu %d %s",
+	TP_printk("%s %ld %d %s",
 		  __entry->rcuname, __entry->gp_seq,
 		  __entry->cpu, __entry->qsevent)
 );

kernel/Makefile

@@ -134,6 +134,8 @@ KASAN_SANITIZE_stackleak.o := n
 KCSAN_SANITIZE_stackleak.o := n
 KCOV_INSTRUMENT_stackleak.o := n
 
+obj-$(CONFIG_SCF_TORTURE_TEST) += scftorture.o
+
 $(obj)/configs.o: $(obj)/config_data.gz
 
 targets += config_data.gz

kernel/entry/common.c

@@ -304,7 +304,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
 	 * terminate a grace period, if and only if the timer interrupt is
 	 * not nested into another interrupt.
 	 *
-	 * Checking for __rcu_is_watching() here would prevent the nesting
+	 * Checking for rcu_is_watching() here would prevent the nesting
 	 * interrupt to invoke rcu_irq_enter(). If that nested interrupt is
 	 * the tick then rcu_flavor_sched_clock_irq() would wrongfully
 	 * assume that it is the first interupt and eventually claim

kernel/locking/locktorture.c

@@ -566,7 +566,7 @@ static struct lock_torture_ops rwsem_lock_ops = {
 #include <linux/percpu-rwsem.h>
 static struct percpu_rw_semaphore pcpu_rwsem;
 
-void torture_percpu_rwsem_init(void)
+static void torture_percpu_rwsem_init(void)
 {
 	BUG_ON(percpu_init_rwsem(&pcpu_rwsem));
 }

kernel/rcu/Kconfig

@@ -135,10 +135,12 @@ config RCU_FANOUT
 
 config RCU_FANOUT_LEAF
 	int "Tree-based hierarchical RCU leaf-level fanout value"
-	range 2 64 if 64BIT
-	range 2 32 if !64BIT
+	range 2 64 if 64BIT && !RCU_STRICT_GRACE_PERIOD
+	range 2 32 if !64BIT && !RCU_STRICT_GRACE_PERIOD
+	range 2 3 if RCU_STRICT_GRACE_PERIOD
 	depends on TREE_RCU && RCU_EXPERT
-	default 16
+	default 16 if !RCU_STRICT_GRACE_PERIOD
+	default 2 if RCU_STRICT_GRACE_PERIOD
 	help
 	  This option controls the leaf-level fanout of hierarchical
 	  implementations of RCU, and allows trading off cache misses

kernel/rcu/Kconfig.debug

@@ -23,7 +23,7 @@ config TORTURE_TEST
 	tristate
 	default n
 
-config RCU_PERF_TEST
+config RCU_SCALE_TEST
 	tristate "performance tests for RCU"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
@@ -114,4 +114,19 @@ config RCU_EQS_DEBUG
 	  Say N here if you need ultimate kernel/user switch latencies
 	  Say Y if you are unsure
 
+config RCU_STRICT_GRACE_PERIOD
+	bool "Provide debug RCU implementation with short grace periods"
+	depends on DEBUG_KERNEL && RCU_EXPERT
+	default n
+	select PREEMPT_COUNT if PREEMPT=n
+	help
+	  Select this option to build an RCU variant that is strict about
+	  grace periods, making them as short as it can.  This limits
+	  scalability, destroys real-time response, degrades battery
+	  lifetime and kills performance.  Don't try this on large
+	  machines, as in systems with more than about 10 or 20 CPUs.
+	  But in conjunction with tools like KASAN, it can be helpful
+	  when looking for certain types of RCU usage bugs, for example,
+	  too-short RCU read-side critical sections.
+
 endmenu # "RCU Debugging"

kernel/rcu/Makefile

@@ -11,7 +11,7 @@ obj-y += update.o sync.o
 obj-$(CONFIG_TREE_SRCU) += srcutree.o
 obj-$(CONFIG_TINY_SRCU) += srcutiny.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
-obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
+obj-$(CONFIG_RCU_SCALE_TEST) += rcuscale.o
 obj-$(CONFIG_RCU_REF_SCALE_TEST) += refscale.o
 obj-$(CONFIG_TREE_RCU) += tree.o
 obj-$(CONFIG_TINY_RCU) += tiny.o

kernel/rcu/rcu_segcblist.c

@@ -475,8 +475,16 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
 	 * Also advance to the oldest segment of callbacks whose
 	 * ->gp_seq[] completion is at or after that passed in via "seq",
 	 * skipping any empty segments.
+	 *
+	 * Note that segment "i" (and any lower-numbered segments
+	 * containing older callbacks) will be unaffected, and their
+	 * grace-period numbers remain unchanged.  For example, if i ==
+	 * WAIT_TAIL, then neither WAIT_TAIL nor DONE_TAIL will be touched.
+	 * Instead, the CBs in NEXT_TAIL will be merged with those in
+	 * NEXT_READY_TAIL and the grace-period number of NEXT_READY_TAIL
+	 * would be updated.  NEXT_TAIL would then be empty.
 	 */
-	if (++i >= RCU_NEXT_TAIL)
+	if (rcu_segcblist_restempty(rsclp, i) || ++i >= RCU_NEXT_TAIL)
 		return false;
 
 	/*

kernel/rcu/rcutorture.c

@@ -52,19 +52,6 @@
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com> and Josh Triplett <josh@joshtriplett.org>");
 
-#ifndef data_race
-#define data_race(expr)							\
-	({								\
-		expr;							\
-	})
-#endif
-#ifndef ASSERT_EXCLUSIVE_WRITER
-#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0)
-#endif
-#ifndef ASSERT_EXCLUSIVE_ACCESS
-#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0)
-#endif
-
 /* Bits for ->extendables field, extendables param, and related definitions. */
 #define RCUTORTURE_RDR_SHIFT	 8	/* Put SRCU index in upper bits. */
 #define RCUTORTURE_RDR_MASK	 ((1 << RCUTORTURE_RDR_SHIFT) - 1)
@@ -100,6 +87,7 @@ torture_param(bool, gp_normal, false,
 	     "Use normal (non-expedited) GP wait primitives");
 torture_param(bool, gp_sync, false, "Use synchronous GP wait primitives");
 torture_param(int, irqreader, 1, "Allow RCU readers from irq handlers");
+torture_param(int, leakpointer, 0, "Leak pointer dereferences from readers");
 torture_param(int, n_barrier_cbs, 0,
 	     "# of callbacks/kthreads for barrier testing");
 torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads");
@@ -185,6 +173,7 @@ static long n_barrier_successes; /* did rcu_barrier test succeed? */
 static unsigned long n_read_exits;
 static struct list_head rcu_torture_removed;
 static unsigned long shutdown_jiffies;
+static unsigned long start_gp_seq;
 
 static int rcu_torture_writer_state;
 #define RTWS_FIXED_DELAY	0
@@ -1413,6 +1402,9 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp)
 	preempt_enable();
 	rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
 	WARN_ON_ONCE(readstate & RCUTORTURE_RDR_MASK);
+	// This next splat is expected behavior if leakpointer, especially
+	// for CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels.
+	WARN_ON_ONCE(leakpointer && READ_ONCE(p->rtort_pipe_count) > 1);
 
 	/* If error or close call, record the sequence of reader protections. */
 	if ((pipe_count > 1 || completed > 1) && !xchg(&err_segs_recorded, 1)) {
@@ -1808,6 +1800,7 @@ struct rcu_fwd {
 	unsigned long rcu_launder_gp_seq_start;
 };
 
+static DEFINE_MUTEX(rcu_fwd_mutex);
 static struct rcu_fwd *rcu_fwds;
 static bool rcu_fwd_emergency_stop;
 
@@ -2074,8 +2067,14 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp)
 static int rcutorture_oom_notify(struct notifier_block *self,
 				 unsigned long notused, void *nfreed)
 {
-	struct rcu_fwd *rfp = rcu_fwds;
+	struct rcu_fwd *rfp;
 
+	mutex_lock(&rcu_fwd_mutex);
+	rfp = rcu_fwds;
+	if (!rfp) {
+		mutex_unlock(&rcu_fwd_mutex);
+		return NOTIFY_OK;
+	}
 	WARN(1, "%s invoked upon OOM during forward-progress testing.\n",
 	     __func__);
 	rcu_torture_fwd_cb_hist(rfp);
@@ -2093,6 +2092,7 @@ static int rcutorture_oom_notify(struct notifier_block *self,
 	smp_mb(); /* Frees before return to avoid redoing OOM. */
 	(*(unsigned long *)nfreed)++; /* Forward progress CBs freed! */
 	pr_info("%s returning after OOM processing.\n", __func__);
+	mutex_unlock(&rcu_fwd_mutex);
 	return NOTIFY_OK;
 }
 
@@ -2114,13 +2114,11 @@ static int rcu_torture_fwd_prog(void *args)
 	do {
 		schedule_timeout_interruptible(fwd_progress_holdoff * HZ);
 		WRITE_ONCE(rcu_fwd_emergency_stop, false);
-		register_oom_notifier(&rcutorture_oom_nb);
 		if (!IS_ENABLED(CONFIG_TINY_RCU) ||
 		    rcu_inkernel_boot_has_ended())
 			rcu_torture_fwd_prog_nr(rfp, &tested, &tested_tries);
 		if (rcu_inkernel_boot_has_ended())
 			rcu_torture_fwd_prog_cr(rfp);
-		unregister_oom_notifier(&rcutorture_oom_nb);
 
 		/* Avoid slow periods, better to test when busy. */
 		stutter_wait("rcu_torture_fwd_prog");
@@ -2160,9 +2158,26 @@ static int __init rcu_torture_fwd_prog_init(void)
 		return -ENOMEM;
 	spin_lock_init(&rfp->rcu_fwd_lock);
 	rfp->rcu_fwd_cb_tail = &rfp->rcu_fwd_cb_head;
+	mutex_lock(&rcu_fwd_mutex);
+	rcu_fwds = rfp;
+	mutex_unlock(&rcu_fwd_mutex);
+	register_oom_notifier(&rcutorture_oom_nb);
 	return torture_create_kthread(rcu_torture_fwd_prog, rfp, fwd_prog_task);
 }
 
+static void rcu_torture_fwd_prog_cleanup(void)
+{
+	struct rcu_fwd *rfp;
+
+	torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);
+	rfp = rcu_fwds;
+	mutex_lock(&rcu_fwd_mutex);
+	rcu_fwds = NULL;
+	mutex_unlock(&rcu_fwd_mutex);
+	unregister_oom_notifier(&rcutorture_oom_nb);
+	kfree(rfp);
+}
+
 /* Callback function for RCU barrier testing. */
 static void rcu_torture_barrier_cbf(struct rcu_head *rcu)
 {
@@ -2460,7 +2475,7 @@ rcu_torture_cleanup(void)
 	show_rcu_gp_kthreads();
 	rcu_torture_read_exit_cleanup();
 	rcu_torture_barrier_cleanup();
-	torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);
+	rcu_torture_fwd_prog_cleanup();
 	torture_stop_kthread(rcu_torture_stall, stall_task);
 	torture_stop_kthread(rcu_torture_writer, writer_task);
 
@@ -2482,8 +2497,9 @@ rcu_torture_cleanup(void)
 
 	rcutorture_get_gp_data(cur_ops->ttype, &flags, &gp_seq);
 	srcutorture_get_gp_data(cur_ops->ttype, srcu_ctlp, &flags, &gp_seq);
-	pr_alert("%s:  End-test grace-period state: g%lu f%#x\n",
-		 cur_ops->name, gp_seq, flags);
+	pr_alert("%s:  End-test grace-period state: g%ld f%#x total-gps=%ld\n",
+		 cur_ops->name, (long)gp_seq, flags,
+		 rcutorture_seq_diff(gp_seq, start_gp_seq));
 	torture_stop_kthread(rcu_torture_stats, stats_task);
 	torture_stop_kthread(rcu_torture_fqs, fqs_task);
 	if (rcu_torture_can_boost())
@@ -2607,6 +2623,8 @@ rcu_torture_init(void)
 	long i;
 	int cpu;
 	int firsterr = 0;
+	int flags = 0;
+	unsigned long gp_seq = 0;
 	static struct rcu_torture_ops *torture_ops[] = {
 		&rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,
 		&busted_srcud_ops, &tasks_ops, &tasks_rude_ops,
@@ -2649,6 +2667,11 @@ rcu_torture_init(void)
 			nrealreaders = 1;
 	}
 	rcu_torture_print_module_parms(cur_ops, "Start of test");
+	rcutorture_get_gp_data(cur_ops->ttype, &flags, &gp_seq);
+	srcutorture_get_gp_data(cur_ops->ttype, srcu_ctlp, &flags, &gp_seq);
+	start_gp_seq = gp_seq;
+	pr_alert("%s:  Start-test grace-period state: g%ld f%#x\n",
+		 cur_ops->name, (long)gp_seq, flags);
 
 	/* Set up the freelist. */
 

kernel/rcu/refscale.c

@@ -546,9 +546,11 @@ static int main_func(void *arg)
 	// Print the average of all experiments
 	SCALEOUT("END OF TEST. Calculating average duration per loop (nanoseconds)...\n");
 
+	if (!errexit) {
 		buf[0] = 0;
 		strcat(buf, "\n");
 		strcat(buf, "Runs\tTime(ns)\n");
+	}
 
 	for (exp = 0; exp < nruns; exp++) {
 		u64 avg;

kernel/rcu/srcutree.c

@@ -29,19 +29,6 @@
 #include "rcu.h"
 #include "rcu_segcblist.h"
 
-#ifndef data_race
-#define data_race(expr)							\
-	({								\
-		expr;							\
-	})
-#endif
-#ifndef ASSERT_EXCLUSIVE_WRITER
-#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0)
-#endif
-#ifndef ASSERT_EXCLUSIVE_ACCESS
-#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0)
-#endif
-
 /* Holdoff in nanoseconds for auto-expediting. */
 #define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
 static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;

kernel/rcu/tree.h

@@ -156,6 +156,7 @@ struct rcu_data {
 	bool		beenonline;	/* CPU online at least once. */
 	bool		gpwrap;		/* Possible ->gp_seq wrap. */
 	bool		exp_deferred_qs; /* This CPU awaiting a deferred QS? */
+	bool		cpu_started;	/* RCU watching this onlining CPU. */
 	struct rcu_node *mynode;	/* This CPU's leaf of hierarchy */
 	unsigned long grpmask;		/* Mask to apply to leaf qsmask. */
 	unsigned long	ticks_this_gp;	/* The number of scheduling-clock */
@@ -164,6 +165,7 @@ struct rcu_data {
 					/* period it is aware of. */
 	struct irq_work defer_qs_iw;	/* Obtain later scheduler attention. */
 	bool defer_qs_iw_pending;	/* Scheduler attention pending? */
+	struct work_struct strict_work;	/* Schedule readers for strict GPs. */
 
 	/* 2) batch handling */
 	struct rcu_segcblist cblist;	/* Segmented callback list, with */

kernel/rcu/tree_exp.h

@@ -732,11 +732,9 @@ static void rcu_exp_need_qs(void)
 /* Invoked on each online non-idle CPU for expedited quiescent state. */
 static void rcu_exp_handler(void *unused)
 {
-	struct rcu_data *rdp;
-	struct rcu_node *rnp;
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+	struct rcu_node *rnp = rdp->mynode;
 
-	rdp = this_cpu_ptr(&rcu_data);
-	rnp = rdp->mynode;
 	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
 	    __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
 		return;

kernel/rcu/tree_plugin.h

@@ -36,6 +36,8 @@ static void __init rcu_bootup_announce_oddness(void)
 		pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
 	if (IS_ENABLED(CONFIG_PROVE_RCU))
 		pr_info("\tRCU lockdep checking is enabled.\n");
+	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+		pr_info("\tRCU strict (and thus non-scalable) grace periods enabled.\n");
 	if (RCU_NUM_LVLS >= 4)
 		pr_info("\tFour(or more)-level hierarchy is enabled.\n");
 	if (RCU_FANOUT_LEAF != 16)
@@ -374,6 +376,8 @@ void __rcu_read_lock(void)
 	rcu_preempt_read_enter();
 	if (IS_ENABLED(CONFIG_PROVE_LOCKING))
 		WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
+	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread)
+		WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true);
 	barrier();  /* critical section after entry code. */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_lock);
@@ -455,8 +459,14 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 		return;
 	}
 	t->rcu_read_unlock_special.s = 0;
-	if (special.b.need_qs)
+	if (special.b.need_qs) {
+		if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
+			rcu_report_qs_rdp(rdp);
+			udelay(rcu_unlock_delay);
+		} else {
 			rcu_qs();
+		}
+	}
 
 	/*
 	 * Respond to a request by an expedited grace period for a
@@ -768,6 +778,24 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
+/*
+ * If strict grace periods are enabled, and if the calling
+ * __rcu_read_unlock() marks the beginning of a quiescent state, immediately
+ * report that quiescent state and, if requested, spin for a bit.
+ */
+void rcu_read_unlock_strict(void)
+{
+	struct rcu_data *rdp;
+
+	if (!IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
+	   irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
+		return;
+	rdp = this_cpu_ptr(&rcu_data);
+	rcu_report_qs_rdp(rdp);
+	udelay(rcu_unlock_delay);
+}
+EXPORT_SYMBOL_GPL(rcu_read_unlock_strict);
+
 /*
  * Tell them what RCU they are running.
  */
@@ -1926,6 +1954,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 	 * nearest grace period (if any) to wait for next.  The CB kthreads
 	 * and the global grace-period kthread are awakened if needed.
 	 */
+	WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
 	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
 		rcu_nocb_lock_irqsave(rdp, flags);
@@ -2411,13 +2440,12 @@ static void show_rcu_nocb_state(struct rcu_data *rdp)
 		return;
 
 	waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
-	wastimer = timer_pending(&rdp->nocb_timer);
+	wastimer = timer_pending(&rdp->nocb_bypass_timer);
 	wassleep = swait_active(&rdp->nocb_gp_wq);
-	if (!rdp->nocb_defer_wakeup && !rdp->nocb_gp_sleep &&
-	    !waslocked && !wastimer && !wassleep)
+	if (!rdp->nocb_gp_sleep && !waslocked && !wastimer && !wassleep)
 		return;  /* Nothing untowards. */
 
-	pr_info("   !!! %c%c%c%c %c\n",
+	pr_info("   nocb GP activity on CB-only CPU!!! %c%c%c%c %c\n",
 		"lL"[waslocked],
 		"dD"[!!rdp->nocb_defer_wakeup],
 		"tT"[wastimer],

kernel/rcu/tree_stall.h

@@ -158,7 +158,7 @@ static void rcu_stall_kick_kthreads(void)
 {
 	unsigned long j;
 
-	if (!rcu_kick_kthreads)
+	if (!READ_ONCE(rcu_kick_kthreads))
 		return;
 	j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
 	if (time_after(jiffies, j) && rcu_state.gp_kthread &&
@@ -580,7 +580,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 	unsigned long js;
 	struct rcu_node *rnp;
 
-	if ((rcu_stall_is_suppressed() && !rcu_kick_kthreads) ||
+	if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) ||
 	    !rcu_gp_in_progress())
 		return;
 	rcu_stall_kick_kthreads();
@@ -623,7 +623,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 
 		/* We haven't checked in, so go dump stack. */
 		print_cpu_stall(gps);
-		if (rcu_cpu_stall_ftrace_dump)
+		if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
 			rcu_ftrace_dump(DUMP_ALL);
 
 	} else if (rcu_gp_in_progress() &&
@@ -632,7 +632,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 
 		/* They had a few time units to dump stack, so complain. */
 		print_other_cpu_stall(gs2, gps);
-		if (rcu_cpu_stall_ftrace_dump)
+		if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
 			rcu_ftrace_dump(DUMP_ALL);
 	}
 }

kernel/rcu/update.c

@@ -53,19 +53,6 @@
 #endif
 #define MODULE_PARAM_PREFIX "rcupdate."
 
-#ifndef data_race
-#define data_race(expr)							\
-	({								\
-		expr;							\
-	})
-#endif
-#ifndef ASSERT_EXCLUSIVE_WRITER
-#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0)
-#endif
-#ifndef ASSERT_EXCLUSIVE_ACCESS
-#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0)
-#endif
-
 #ifndef CONFIG_TINY_RCU
 module_param(rcu_expedited, int, 0);
 module_param(rcu_normal, int, 0);

kernel/smp.c

@@ -20,6 +20,9 @@
 #include <linux/sched.h>
 #include <linux/sched/idle.h>
 #include <linux/hypervisor.h>
+#include <linux/sched/clock.h>
+#include <linux/nmi.h>
+#include <linux/sched/debug.h>
 
 #include "smpboot.h"
 #include "sched/smp.h"
@@ -96,6 +99,103 @@ void __init call_function_init(void)
 	smpcfd_prepare_cpu(smp_processor_id());
 }
 
+#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
+
+static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
+static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
+static DEFINE_PER_CPU(void *, cur_csd_info);
+
+#define CSD_LOCK_TIMEOUT (5ULL * NSEC_PER_SEC)
+static atomic_t csd_bug_count = ATOMIC_INIT(0);
+
+/* Record current CSD work for current CPU, NULL to erase. */
+static void csd_lock_record(call_single_data_t *csd)
+{
+	if (!csd) {
+		smp_mb(); /* NULL cur_csd after unlock. */
+		__this_cpu_write(cur_csd, NULL);
+		return;
+	}
+	__this_cpu_write(cur_csd_func, csd->func);
+	__this_cpu_write(cur_csd_info, csd->info);
+	smp_wmb(); /* func and info before csd. */
+	__this_cpu_write(cur_csd, csd);
+	smp_mb(); /* Update cur_csd before function call. */
+		  /* Or before unlock, as the case may be. */
+}
+
+static __always_inline int csd_lock_wait_getcpu(call_single_data_t *csd)
+{
+	unsigned int csd_type;
+
+	csd_type = CSD_TYPE(csd);
+	if (csd_type == CSD_TYPE_ASYNC || csd_type == CSD_TYPE_SYNC)
+		return csd->dst; /* Other CSD_TYPE_ values might not have ->dst. */
+	return -1;
+}
+
+/*
+ * Complain if too much time spent waiting.  Note that only
+ * the CSD_TYPE_SYNC/ASYNC types provide the destination CPU,
+ * so waiting on other types gets much less information.
+ */
+static __always_inline bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, int *bug_id)
+{
+	int cpu = -1;
+	int cpux;
+	bool firsttime;
+	u64 ts2, ts_delta;
+	call_single_data_t *cpu_cur_csd;
+	unsigned int flags = READ_ONCE(csd->flags);
+
+	if (!(flags & CSD_FLAG_LOCK)) {
+		if (!unlikely(*bug_id))
+			return true;
+		cpu = csd_lock_wait_getcpu(csd);
+		pr_alert("csd: CSD lock (#%d) got unstuck on CPU#%02d, CPU#%02d released the lock.\n",
+			 *bug_id, raw_smp_processor_id(), cpu);
+		return true;
+	}
+
+	ts2 = sched_clock();
+	ts_delta = ts2 - *ts1;
+	if (likely(ts_delta <= CSD_LOCK_TIMEOUT))
+		return false;
+
+	firsttime = !*bug_id;
+	if (firsttime)
+		*bug_id = atomic_inc_return(&csd_bug_count);
+	cpu = csd_lock_wait_getcpu(csd);
+	if (WARN_ONCE(cpu < 0 || cpu >= nr_cpu_ids, "%s: cpu = %d\n", __func__, cpu))
+		cpux = 0;
+	else
+		cpux = cpu;
+	cpu_cur_csd = smp_load_acquire(&per_cpu(cur_csd, cpux)); /* Before func and info. */
+	pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %llu ns for CPU#%02d %pS(%ps).\n",
+		 firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), ts2 - ts0,
+		 cpu, csd->func, csd->info);
+	if (cpu_cur_csd && csd != cpu_cur_csd) {
+		pr_alert("\tcsd: CSD lock (#%d) handling prior %pS(%ps) request.\n",
+			 *bug_id, READ_ONCE(per_cpu(cur_csd_func, cpux)),
+			 READ_ONCE(per_cpu(cur_csd_info, cpux)));
+	} else {
+		pr_alert("\tcsd: CSD lock (#%d) %s.\n",
+			 *bug_id, !cpu_cur_csd ? "unresponsive" : "handling this request");
+	}
+	if (cpu >= 0) {
+		if (!trigger_single_cpu_backtrace(cpu))
+			dump_cpu_task(cpu);
+		if (!cpu_cur_csd) {
+			pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\n", *bug_id, raw_smp_processor_id(), cpu);
+			arch_send_call_function_single_ipi(cpu);
+		}
+	}
+	dump_stack();
+	*ts1 = ts2;
+
+	return false;
+}
+
 /*
  * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
  *
@@ -103,10 +203,30 @@ void __init call_function_init(void)
  * previous function call. For multi-cpu calls its even more interesting
  * as we'll have to ensure no other cpu is observing our csd.
  */
+static __always_inline void csd_lock_wait(call_single_data_t *csd)
+{
+	int bug_id = 0;
+	u64 ts0, ts1;
+
+	ts1 = ts0 = sched_clock();
+	for (;;) {
+		if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id))
+			break;
+		cpu_relax();
+	}
+	smp_acquire__after_ctrl_dep();
+}
+
+#else
+static void csd_lock_record(call_single_data_t *csd)
+{
+}
+
 static __always_inline void csd_lock_wait(call_single_data_t *csd)
 {
 	smp_cond_load_acquire(&csd->flags, !(VAL & CSD_FLAG_LOCK));
 }
+#endif
 
 static __always_inline void csd_lock(call_single_data_t *csd)
 {
@@ -166,9 +286,11 @@ static int generic_exec_single(int cpu, call_single_data_t *csd)
 		 * We can unlock early even for the synchronous on-stack case,
 		 * since we're doing this from the same CPU..
 		 */
+		csd_lock_record(csd);
 		csd_unlock(csd);
 		local_irq_save(flags);
 		func(info);
+		csd_lock_record(NULL);
 		local_irq_restore(flags);
 		return 0;
 	}
@@ -268,8 +390,10 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
 				entry = &csd_next->llist;
 			}
 
+			csd_lock_record(csd);
 			func(info);
 			csd_unlock(csd);
+			csd_lock_record(NULL);
 		} else {
 			prev = &csd->llist;
 		}
@@ -296,8 +420,10 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
 				smp_call_func_t func = csd->func;
 				void *info = csd->info;
 
+				csd_lock_record(csd);
 				csd_unlock(csd);
 				func(info);
+				csd_lock_record(NULL);
 			} else if (type == CSD_TYPE_IRQ_WORK) {
 				irq_work_single(csd);
 			}
@@ -375,6 +501,10 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
 
 	csd->func = func;
 	csd->info = info;
+#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
+	csd->src = smp_processor_id();
+	csd->dst = cpu;
+#endif
 
 	err = generic_exec_single(cpu, csd);
 
@@ -540,6 +670,10 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
 			csd->flags |= CSD_TYPE_SYNC;
 		csd->func = func;
 		csd->info = info;
+#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
+		csd->src = smp_processor_id();
+		csd->dst = cpu;
+#endif
 		if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
 			__cpumask_set_cpu(cpu, cfd->cpumask_ipi);
 	}

kernel/time/tick-sched.c

@@ -927,7 +927,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 
 		if (ratelimit < 10 &&
 		    (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
-			pr_warn("NOHZ: local_softirq_pending %02x\n",
+			pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x!!!\n",
 				(unsigned int) local_softirq_pending());
 			ratelimit++;
 		}

lib/Kconfig.debug

@@ -1367,6 +1367,27 @@ config WW_MUTEX_SELFTEST
 	  Say M if you want these self tests to build as a module.
 	  Say N if you are unsure.
 
+config SCF_TORTURE_TEST
+	tristate "torture tests for smp_call_function*()"
+	depends on DEBUG_KERNEL
+	select TORTURE_TEST
+	help
+	  This option provides a kernel module that runs torture tests
+	  on the smp_call_function() family of primitives.  The kernel
+	  module may be built after the fact on the running kernel to
+	  be tested, if desired.
+
+config CSD_LOCK_WAIT_DEBUG
+	bool "Debugging for csd_lock_wait(), called from smp_call_function*()"
+	depends on DEBUG_KERNEL
+	depends on 64BIT
+	default n
+	help
+	  This option enables debug prints when CPUs are slow to respond
+	  to the smp_call_function*() IPI wrappers.  These debug prints
+	  include the IPI handler function currently executing (if any)
+	  and relevant stack traces.
+
 endmenu # lock debugging
 
 config TRACE_IRQFLAGS

lib/nmi_backtrace.c

@@ -85,12 +85,16 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
 	put_cpu();
 }
 
+// Dump stacks even for idle CPUs.
+static bool backtrace_idle;
+module_param(backtrace_idle, bool, 0644);
+
 bool nmi_cpu_backtrace(struct pt_regs *regs)
 {
 	int cpu = smp_processor_id();
 
 	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
-		if (regs && cpu_in_idle(instruction_pointer(regs))) {
+		if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
 			pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
 				cpu, (void *)instruction_pointer(regs));
 		} else {

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuperf-ftrace.sh → tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuscale-ftrace.sh

 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0+
 #
-# Analyze a given results directory for rcuperf performance measurements,
+# Analyze a given results directory for rcuscale performance measurements,
 # looking for ftrace data.  Exits with 0 if data was found, analyzed, and
-# printed.  Intended to be invoked from kvm-recheck-rcuperf.sh after
+# printed.  Intended to be invoked from kvm-recheck-rcuscale.sh after
 # argument checking.
 #
-# Usage: kvm-recheck-rcuperf-ftrace.sh resdir
+# Usage: kvm-recheck-rcuscale-ftrace.sh resdir
 #
 # Copyright (C) IBM Corporation, 2016
 #

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuperf.sh → tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuscale.sh

 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0+
 #
-# Analyze a given results directory for rcuperf performance measurements.
+# Analyze a given results directory for rcuscale scalability measurements.
 #
-# Usage: kvm-recheck-rcuperf.sh resdir
+# Usage: kvm-recheck-rcuscale.sh resdir
 #
 # Copyright (C) IBM Corporation, 2016
 #
@@ -20,7 +20,7 @@ fi
 PATH=`pwd`/tools/testing/selftests/rcutorture/bin:$PATH; export PATH
 . functions.sh
 
-if kvm-recheck-rcuperf-ftrace.sh $i
+if kvm-recheck-rcuscale-ftrace.sh $i
 then
 	# ftrace data was successfully analyzed, call it good!
 	exit 0
@@ -30,12 +30,12 @@ configfile=`echo $i | sed -e 's/^.*\///'`
 
 sed -e 's/^\[[^]]*]//' < $i/console.log |
 awk '
-/-perf: .* gps: .* batches:/ {
+/-scale: .* gps: .* batches:/ {
 	ngps = $9;
 	nbatches = $11;
 }
 
-/-perf: .*writer-duration/ {
+/-scale: .*writer-duration/ {
 	gptimes[++n] = $5 / 1000.;
 	sum += $5 / 1000.;
 }
@@ -43,7 +43,7 @@ awk '
 END {
 	newNR = asort(gptimes);
 	if (newNR <= 0) {
-		print "No rcuperf records found???"
+		print "No rcuscale records found???"
 		exit;
 	}
 	pct50 = int(newNR * 50 / 100);
@@ -79,5 +79,5 @@ END {
 	print "99th percentile grace-period duration: " gptimes[pct99];
 	print "Maximum grace-period duration: " gptimes[newNR];
 	print "Grace periods: " ngps + 0 " Batches: " nbatches + 0 " Ratio: " ngps / nbatches;
-	print "Computed from rcuperf printk output.";
+	print "Computed from rcuscale printk output.";
 }'

tools/testing/selftests/rcutorture/bin/kvm-recheck-scf.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Analyze a given results directory for rcutorture progress.
+#
+# Usage: kvm-recheck-rcu.sh resdir
+#
+# Copyright (C) Facebook, 2020
+#
+# Authors: Paul E. McKenney <paulmck@kernel.org>
+
+i="$1"
+if test -d "$i" -a -r "$i"
+then
+	:
+else
+	echo Unreadable results directory: $i
+	exit 1
+fi
+. functions.sh
+
+configfile=`echo $i | sed -e 's/^.*\///'`
+nscfs="`grep 'scf_invoked_count ver:' $i/console.log 2> /dev/null | tail -1 | sed -e 's/^.* scf_invoked_count ver: //' -e 's/ .*$//' | tr -d '\015'`"
+if test -z "$nscfs"
+then
+	echo "$configfile ------- "
+else
+	dur="`sed -e 's/^.* scftorture.shutdown_secs=//' -e 's/ .*$//' < $i/qemu-cmd 2> /dev/null`"
+	if test -z "$dur"
+	then
+		rate=""
+	else
+		nscfss=`awk -v nscfs=$nscfs -v dur=$dur '
+			BEGIN { print nscfs / dur }' < /dev/null`
+		rate=" ($nscfss/s)"
+	fi
+	echo "${configfile} ------- ${nscfs} SCF handler invocations$rate"
+fi

tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh

@@ -66,6 +66,7 @@ config_override_param () {
 echo > $T/KcList
 config_override_param "$config_dir/CFcommon" KcList "`cat $config_dir/CFcommon 2> /dev/null`"
 config_override_param "$config_template" KcList "`cat $config_template 2> /dev/null`"
+config_override_param "--gdb options" KcList "$TORTURE_KCONFIG_GDB_ARG"
 config_override_param "--kasan options" KcList "$TORTURE_KCONFIG_KASAN_ARG"
 config_override_param "--kcsan options" KcList "$TORTURE_KCONFIG_KCSAN_ARG"
 config_override_param "--kconfig argument" KcList "$TORTURE_KCONFIG_ARG"
@@ -152,7 +153,11 @@ qemu_append="`identify_qemu_append "$QEMU"`"
 boot_args="`configfrag_boot_params "$boot_args" "$config_template"`"
 # Generate kernel-version-specific boot parameters
 boot_args="`per_version_boot_params "$boot_args" $resdir/.config $seconds`"
-echo $QEMU $qemu_args -m $TORTURE_QEMU_MEM -kernel $KERNEL -append \"$qemu_append $boot_args\" > $resdir/qemu-cmd
+if test -n "$TORTURE_BOOT_GDB_ARG"
+then
+	boot_args="$boot_args $TORTURE_BOOT_GDB_ARG"
+fi
+echo $QEMU $qemu_args -m $TORTURE_QEMU_MEM -kernel $KERNEL -append \"$qemu_append $boot_args\" $TORTURE_QEMU_GDB_ARG > $resdir/qemu-cmd
 
 if test -n "$TORTURE_BUILDONLY"
 then
@@ -171,14 +176,26 @@ echo "NOTE: $QEMU either did not run or was interactive" > $resdir/console.log
 # Attempt to run qemu
 ( . $T/qemu-cmd; wait `cat  $resdir/qemu_pid`; echo $? > $resdir/qemu-retval ) &
 commandcompleted=0
-sleep 10 # Give qemu's pid a chance to reach the file
-if test -s "$resdir/qemu_pid"
+if test -z "$TORTURE_KCONFIG_GDB_ARG"
 then
+	sleep 10 # Give qemu's pid a chance to reach the file
+	if test -s "$resdir/qemu_pid"
+	then
 		qemu_pid=`cat "$resdir/qemu_pid"`
 		echo Monitoring qemu job at pid $qemu_pid
-else
+	else
 		qemu_pid=""
 		echo Monitoring qemu job at yet-as-unknown pid
+	fi
+fi
+if test -n "$TORTURE_KCONFIG_GDB_ARG"
+then
+	echo Waiting for you to attach a debug session, for example: > /dev/tty
+	echo "    gdb $base_resdir/vmlinux" > /dev/tty
+	echo 'After symbols load and the "(gdb)" prompt appears:' > /dev/tty
+	echo "    target remote :1234" > /dev/tty
+	echo "    continue" > /dev/tty
+	kstarttime=`gawk 'BEGIN { print systime() }' < /dev/null`
 fi
 while :
 do

tools/testing/selftests/rcutorture/bin/kvm.sh

@@ -31,6 +31,9 @@ TORTURE_DEFCONFIG=defconfig
 TORTURE_BOOT_IMAGE=""
 TORTURE_INITRD="$KVM/initrd"; export TORTURE_INITRD
 TORTURE_KCONFIG_ARG=""
+TORTURE_KCONFIG_GDB_ARG=""
+TORTURE_BOOT_GDB_ARG=""
+TORTURE_QEMU_GDB_ARG=""
 TORTURE_KCONFIG_KASAN_ARG=""
 TORTURE_KCONFIG_KCSAN_ARG=""
 TORTURE_KMAKE_ARG=""
@@ -46,6 +49,7 @@ jitter="-1"
 
 usage () {
 	echo "Usage: $scriptname optional arguments:"
+	echo "       --allcpus"
 	echo "       --bootargs kernel-boot-arguments"
 	echo "       --bootimage relative-path-to-kernel-boot-image"
 	echo "       --buildonly"
@@ -55,17 +59,19 @@ usage () {
 	echo "       --defconfig string"
 	echo "       --dryrun sched|script"
 	echo "       --duration minutes"
+	echo "       --gdb"
+	echo "       --help"
 	echo "       --interactive"
 	echo "       --jitter N [ maxsleep (us) [ maxspin (us) ] ]"
 	echo "       --kconfig Kconfig-options"
 	echo "       --kmake-arg kernel-make-arguments"
 	echo "       --mac nn:nn:nn:nn:nn:nn"
-	echo "       --memory megabytes | nnnG"
+	echo "       --memory megabytes|nnnG"
 	echo "       --no-initrd"
 	echo "       --qemu-args qemu-arguments"
 	echo "       --qemu-cmd qemu-system-..."
 	echo "       --results absolute-pathname"
-	echo "       --torture rcu"
+	echo "       --torture lock|rcu|rcuscale|refscale|scf"
 	echo "       --trust-make"
 	exit 1
 }
@@ -126,6 +132,14 @@ do
 		dur=$(($2*60))
 		shift
 		;;
+	--gdb)
+		TORTURE_KCONFIG_GDB_ARG="CONFIG_DEBUG_INFO=y"; export TORTURE_KCONFIG_GDB_ARG
+		TORTURE_BOOT_GDB_ARG="nokaslr"; export TORTURE_BOOT_GDB_ARG
+		TORTURE_QEMU_GDB_ARG="-s -S"; export TORTURE_QEMU_GDB_ARG
+		;;
+	--help|-h)
+		usage
+		;;
 	--interactive)
 		TORTURE_QEMU_INTERACTIVE=1; export TORTURE_QEMU_INTERACTIVE
 		;;
@@ -184,13 +198,13 @@ do
 		shift
 		;;
 	--torture)
-		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuperf\|refscale\)$' '^--'
+		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuscale\|refscale\|scf\)$' '^--'
 		TORTURE_SUITE=$2
 		shift
-		if test "$TORTURE_SUITE" = rcuperf || test "$TORTURE_SUITE" = refscale
+		if test "$TORTURE_SUITE" = rcuscale || test "$TORTURE_SUITE" = refscale
 		then
 			# If you really want jitter for refscale or
-			# rcuperf, specify it after specifying the rcuperf
+			# rcuscale, specify it after specifying the rcuscale
 			# or the refscale.  (But why jitter in these cases?)
 			jitter=0
 		fi
@@ -248,6 +262,15 @@ do
 done
 touch $T/cfgcpu
 configs_derep="`echo $configs_derep | sed -e "s/\<CFLIST\>/$defaultconfigs/g"`"
+if test -n "$TORTURE_KCONFIG_GDB_ARG"
+then
+	if test "`echo $configs_derep | wc -w`" -gt 1
+	then
+		echo "The --config list is: $configs_derep."
+		echo "Only one --config permitted with --gdb, terminating."
+		exit 1
+	fi
+fi
 for CF1 in $configs_derep
 do
 	if test -f "$CONFIGFRAG/$CF1"
@@ -323,6 +346,9 @@ TORTURE_BUILDONLY="$TORTURE_BUILDONLY"; export TORTURE_BUILDONLY
 TORTURE_DEFCONFIG="$TORTURE_DEFCONFIG"; export TORTURE_DEFCONFIG
 TORTURE_INITRD="$TORTURE_INITRD"; export TORTURE_INITRD
 TORTURE_KCONFIG_ARG="$TORTURE_KCONFIG_ARG"; export TORTURE_KCONFIG_ARG
+TORTURE_KCONFIG_GDB_ARG="$TORTURE_KCONFIG_GDB_ARG"; export TORTURE_KCONFIG_GDB_ARG
+TORTURE_BOOT_GDB_ARG="$TORTURE_BOOT_GDB_ARG"; export TORTURE_BOOT_GDB_ARG
+TORTURE_QEMU_GDB_ARG="$TORTURE_QEMU_GDB_ARG"; export TORTURE_QEMU_GDB_ARG
 TORTURE_KCONFIG_KASAN_ARG="$TORTURE_KCONFIG_KASAN_ARG"; export TORTURE_KCONFIG_KASAN_ARG
 TORTURE_KCONFIG_KCSAN_ARG="$TORTURE_KCONFIG_KCSAN_ARG"; export TORTURE_KCONFIG_KCSAN_ARG
 TORTURE_KMAKE_ARG="$TORTURE_KMAKE_ARG"; export TORTURE_KMAKE_ARG

tools/testing/selftests/rcutorture/bin/parse-console.sh

@@ -33,8 +33,8 @@ then
 fi
 cat /dev/null > $file.diags
 
-# Check for proper termination, except for rcuperf and refscale.
-if test "$TORTURE_SUITE" != rcuperf && test "$TORTURE_SUITE" != refscale
+# Check for proper termination, except for rcuscale and refscale.
+if test "$TORTURE_SUITE" != rcuscale && test "$TORTURE_SUITE" != refscale
 then
 	# check for abject failure
 
@@ -67,6 +67,7 @@ then
 	grep --binary-files=text 'torture:.*ver:' $file |
 	egrep --binary-files=text -v '\(null\)|rtc: 000000000* ' |
 	sed -e 's/^(initramfs)[^]]*] //' -e 's/^\[[^]]*] //' |
+	sed -e 's/^.*ver: //' |
 	awk '
 	BEGIN	{
 		ver = 0;
@@ -74,13 +75,13 @@ then
 		}
 
 		{
-		if (!badseq && ($5 + 0 != $5 || $5 <= ver)) {
+		if (!badseq && ($1 + 0 != $1 || $1 <= ver)) {
 			badseqno1 = ver;
-			badseqno2 = $5;
+			badseqno2 = $1;
 			badseqnr = NR;
 			badseq = 1;
 		}
-		ver = $5
+		ver = $1
 		}
 
 	END	{

tools/testing/selftests/rcutorture/configs/rcu/TREE05

@@ -16,5 +16,6 @@ CONFIG_RCU_NOCB_CPU=y
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
+CONFIG_PROVE_RCU_LIST=y
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcuperf/CFcommon → tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon

-CONFIG_RCU_PERF_TEST=y
+CONFIG_RCU_SCALE_TEST=y
 CONFIG_PRINTK_TIME=y

tools/testing/selftests/rcutorture/configs/rcuperf/ver_functions.sh → tools/testing/selftests/rcutorture/configs/rcuscale/ver_functions.sh

@@ -11,6 +11,6 @@
 #
 # Adds per-version torture-module parameters to kernels supporting them.
 per_version_boot_params () {
-	echo $1 rcuperf.shutdown=1 \
-		rcuperf.verbose=1
+	echo $1 rcuscale.shutdown=1 \
+		rcuscale.verbose=1
 }

tools/testing/selftests/rcutorture/configs/scf/CFLIST

+NOPREEMPT
+PREEMPT

tools/testing/selftests/rcutorture/configs/scf/CFcommon

+CONFIG_SCF_TORTURE_TEST=y
+CONFIG_PRINTK_TIME=y

tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT

+CONFIG_SMP=y
+CONFIG_PREEMPT_NONE=y
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=n
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=n
+CONFIG_NO_HZ_FULL=y
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_PROVE_LOCKING=n

tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT.boot

+nohz_full=1

tools/testing/selftests/rcutorture/configs/scf/PREEMPT

+CONFIG_SMP=y
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=y
+CONFIG_NO_HZ_FULL=n
+CONFIG_DEBUG_LOCK_ALLOC=y
+CONFIG_PROVE_LOCKING=y

tools/testing/selftests/rcutorture/configs/scf/ver_functions.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Torture-suite-dependent shell functions for the rest of the scripts.
+#
+# Copyright (C) Facebook, 2020
+#
+# Authors: Paul E. McKenney <paulmck@kernel.org>
+
+# scftorture_param_onoff bootparam-string config-file
+#
+# Adds onoff scftorture module parameters to kernels having it.
+scftorture_param_onoff () {
+	if ! bootparam_hotplug_cpu "$1" && configfrag_hotplug_cpu "$2"
+	then
+		echo CPU-hotplug kernel, adding scftorture onoff. 1>&2
+		echo scftorture.onoff_interval=1000 scftorture.onoff_holdoff=30
+	fi
+}
+
+# per_version_boot_params bootparam-string config-file seconds
+#
+# Adds per-version torture-module parameters to kernels supporting them.
+per_version_boot_params () {
+	echo $1 `scftorture_param_onoff "$1" "$2"` \
+		scftorture.stat_interval=15 \
+		scftorture.shutdown_secs=$3 \
+		scftorture.verbose=1 \
+		scf
+}

tools/testing/selftests/rcutorture/doc/initrd.txt

-The rcutorture scripting tools automatically create the needed initrd
-directory using dracut.  Failing that, this tool will create an initrd
-containing a single statically linked binary named "init" that loops
-over a very long sleep() call.  In both cases, this creation is done
-by tools/testing/selftests/rcutorture/bin/mkinitrd.sh.
+The rcutorture scripting tools automatically create an initrd containing
+a single statically linked binary named "init" that loops over a
+very long sleep() call.  In both cases, this creation is done by
+tools/testing/selftests/rcutorture/bin/mkinitrd.sh.
 
-However, if you are attempting to run rcutorture on a system that does
-not have dracut installed, and if you don't like the notion of static
-linking, you might wish to press an existing initrd into service:
+However, if you don't like the notion of statically linked bare-bones
+userspace environments, you might wish to press an existing initrd
+into service:
 
 ------------------------------------------------------------------------
 cd tools/testing/selftests/rcutorture
@@ -15,24 +14,3 @@ mkdir initrd
 cd initrd
 cpio -id < /tmp/initrd.img.zcat
 # Manually verify that initrd contains needed binaries and libraries.
-------------------------------------------------------------------------
-
-Interestingly enough, if you are running rcutorture, you don't really
-need userspace in many cases.  Running without userspace has the
-advantage of allowing you to test your kernel independently of the
-distro in place, the root-filesystem layout, and so on.  To make this
-happen, put the following script in the initrd's tree's "/init" file,
-with 0755 mode.
-
-------------------------------------------------------------------------
-#!/bin/sh
-
-while :
-do
-	sleep 10
-done
-------------------------------------------------------------------------
-
-This approach also allows most of the binaries and libraries in the
-initrd filesystem to be dispensed with, which can save significant
-space in rcutorture's "res" directory.

tools/testing/selftests/rcutorture/doc/rcu-test-image.txt

-This document describes one way to create the rcu-test-image file
-that contains the filesystem used by the guest-OS kernel.  There are
-probably much better ways of doing this, and this filesystem could no
-doubt be smaller.  It is probably also possible to simply download
-an appropriate image from any number of places.
+Normally, a minimal initrd is created automatically by the rcutorture
+scripting.  But minimal really does mean "minimal", namely just a single
+root directory with a single statically linked executable named "init":
+
+$ size tools/testing/selftests/rcutorture/initrd/init
+   text    data     bss     dec     hex filename
+    328       0       8     336     150 tools/testing/selftests/rcutorture/initrd/init
+
+Suppose you need to run some scripts, perhaps to monitor or control
+some aspect of the rcutorture testing.  This will require a more fully
+filled-out userspace, perhaps containing libraries, executables for
+the shell and other utilities, and soforth.  In that case, place your
+desired filesystem here:
+
+	tools/testing/selftests/rcutorture/initrd
+
+For example, your tools/testing/selftests/rcutorture/initrd/init might
+be a script that does any needed mount operations and starts whatever
+scripts need starting to properly monitor or control your testing.
+The next rcutorture build will then incorporate this filesystem into
+the kernel image that is passed to qemu.
+
+Or maybe you need a real root filesystem for some reason, in which case
+please read on!
+
+The remainder of this document describes one way to create the
+rcu-test-image file that contains the filesystem used by the guest-OS
+kernel.  There are probably much better ways of doing this, and this
+filesystem could no doubt be smaller.  It is probably also possible to
+simply download an appropriate image from any number of places.
 
 That said, here are the commands:
 
@@ -36,7 +61,7 @@ References:
 	https://help.ubuntu.com/community/JeOSVMBuilder
 	http://wiki.libvirt.org/page/UbuntuKVMWalkthrough
 	http://www.moe.co.uk/2011/01/07/pci_add_option_rom-failed-to-find-romfile-pxe-rtl8139-bin/ -- "apt-get install kvm-pxe"
-	http://www.landley.net/writing/rootfs-howto.html
-	http://en.wikipedia.org/wiki/Initrd
-	http://en.wikipedia.org/wiki/Cpio
+	https://www.landley.net/writing/rootfs-howto.html
+	https://en.wikipedia.org/wiki/Initrd
+	https://en.wikipedia.org/wiki/Cpio
 	http://wiki.libvirt.org/page/UbuntuKVMWalkthrough