lockdep: Annotate irq_work

Mark irq_work items with IRQ_WORK_HARD_IRQ which should be invoked in
hardirq context even on PREEMPT_RT. IRQ_WORK without this flag will be
invoked in softirq context on PREEMPT_RT.

Set ->irq_config to 1 for the IRQ_WORK items which are invoked in softirq
context so lockdep knows that these can safely acquire a spinlock_t.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.643576700@linutronix.de

include/linux/irq_work.h

@@ -18,6 +18,8 @@
 
 /* Doesn't want IPI, wait for tick: */
 #define IRQ_WORK_LAZY		BIT(2)
+/* Run hard IRQ context, even on RT */
+#define IRQ_WORK_HARD_IRQ	BIT(3)
 
 #define IRQ_WORK_CLAIMED	(IRQ_WORK_PENDING | IRQ_WORK_BUSY)
 

include/linux/irqflags.h

@@ -69,6 +69,17 @@ do {						\
 			current->irq_config = 0;	\
 	  } while (0)
 
+# define lockdep_irq_work_enter(__work)					\
+	  do {								\
+		  if (!(atomic_read(&__work->flags) & IRQ_WORK_HARD_IRQ))\
+			current->irq_config = 1;			\
+	  } while (0)
+# define lockdep_irq_work_exit(__work)					\
+	  do {								\
+		  if (!(atomic_read(&__work->flags) & IRQ_WORK_HARD_IRQ))\
+			current->irq_config = 0;			\
+	  } while (0)
+
 #else
 # define trace_hardirqs_on()		do { } while (0)
 # define trace_hardirqs_off()		do { } while (0)
@@ -83,6 +94,8 @@ do {						\
 # define lockdep_softirq_exit()		do { } while (0)
 # define lockdep_hrtimer_enter(__hrtimer)		do { } while (0)
 # define lockdep_hrtimer_exit(__hrtimer)		do { } while (0)
+# define lockdep_irq_work_enter(__work)		do { } while (0)
+# define lockdep_irq_work_exit(__work)		do { } while (0)
 #endif
 
 #if defined(CONFIG_IRQSOFF_TRACER) || \

kernel/irq_work.c

@@ -153,7 +153,9 @@ static void irq_work_run_list(struct llist_head *list)
 		 */
 		flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags);
 
+		lockdep_irq_work_enter(work);
 		work->func(work);
+		lockdep_irq_work_exit(work);
 		/*
 		 * Clear the BUSY bit and return to the free state if
 		 * no-one else claimed it meanwhile.

kernel/rcu/tree.c

@@ -1113,6 +1113,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 		    !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
 		    (rnp->ffmask & rdp->grpmask)) {
 			init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
+			atomic_set(&rdp->rcu_iw.flags, IRQ_WORK_HARD_IRQ);
 			rdp->rcu_iw_pending = true;
 			rdp->rcu_iw_gp_seq = rnp->gp_seq;
 			irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);

kernel/time/tick-sched.c

@@ -245,6 +245,7 @@ static void nohz_full_kick_func(struct irq_work *work)
 
 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
 	.func = nohz_full_kick_func,
+	.flags = ATOMIC_INIT(IRQ_WORK_HARD_IRQ),
 };
 
 /*