Commit 80a7956f authored by Paul E. McKenney's avatar Paul E. McKenney

srcu: Merge ->srcu_state into ->srcu_gp_seq

Updating ->srcu_state and ->srcu_gp_seq will lead to extremely complex
race conditions given multiple callback queues, so this commit takes
advantage of the two-bit state now available in rcu_seq counters to
store the state in the bottom two bits of ->srcu_gp_seq.
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent f1ec57a4
...@@ -43,8 +43,7 @@ struct srcu_struct { ...@@ -43,8 +43,7 @@ struct srcu_struct {
unsigned long completed; unsigned long completed;
unsigned long srcu_gp_seq; unsigned long srcu_gp_seq;
struct srcu_array __percpu *per_cpu_ref; struct srcu_array __percpu *per_cpu_ref;
spinlock_t queue_lock; /* protect ->srcu_cblist, ->srcu_state */ spinlock_t queue_lock; /* protect ->srcu_cblist */
int srcu_state;
struct rcu_segcblist srcu_cblist; struct rcu_segcblist srcu_cblist;
struct delayed_work work; struct delayed_work work;
#ifdef CONFIG_DEBUG_LOCK_ALLOC #ifdef CONFIG_DEBUG_LOCK_ALLOC
...@@ -56,7 +55,6 @@ struct srcu_struct { ...@@ -56,7 +55,6 @@ struct srcu_struct {
#define SRCU_STATE_IDLE 0 #define SRCU_STATE_IDLE 0
#define SRCU_STATE_SCAN1 1 #define SRCU_STATE_SCAN1 1
#define SRCU_STATE_SCAN2 2 #define SRCU_STATE_SCAN2 2
#define SRCU_STATE_DONE 3
#ifdef CONFIG_DEBUG_LOCK_ALLOC #ifdef CONFIG_DEBUG_LOCK_ALLOC
...@@ -85,7 +83,6 @@ void process_srcu(struct work_struct *work); ...@@ -85,7 +83,6 @@ void process_srcu(struct work_struct *work);
.completed = -300, \ .completed = -300, \
.per_cpu_ref = &name##_srcu_array, \ .per_cpu_ref = &name##_srcu_array, \
.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \ .queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
.srcu_state = SRCU_STATE_IDLE, \
.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\ .srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\
.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\ .work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
__SRCU_DEP_MAP_INIT(name) \ __SRCU_DEP_MAP_INIT(name) \
......
...@@ -82,6 +82,16 @@ static inline int rcu_seq_state(unsigned long s) ...@@ -82,6 +82,16 @@ static inline int rcu_seq_state(unsigned long s)
return s & RCU_SEQ_STATE_MASK; return s & RCU_SEQ_STATE_MASK;
} }
/*
* Set the state portion of the pointed-to sequence number.
* The caller is responsible for preventing conflicting updates.
*/
static inline void rcu_seq_set_state(unsigned long *sp, int newstate)
{
WARN_ON_ONCE(newstate & ~RCU_SEQ_STATE_MASK);
WRITE_ONCE(*sp, (*sp & ~RCU_SEQ_STATE_MASK) + newstate);
}
/* Adjust sequence number for start of update-side operation. */ /* Adjust sequence number for start of update-side operation. */
static inline void rcu_seq_start(unsigned long *sp) static inline void rcu_seq_start(unsigned long *sp)
{ {
......
...@@ -44,7 +44,6 @@ static int init_srcu_struct_fields(struct srcu_struct *sp) ...@@ -44,7 +44,6 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
sp->completed = 0; sp->completed = 0;
sp->srcu_gp_seq = 0; sp->srcu_gp_seq = 0;
spin_lock_init(&sp->queue_lock); spin_lock_init(&sp->queue_lock);
sp->srcu_state = SRCU_STATE_IDLE;
rcu_segcblist_init(&sp->srcu_cblist); rcu_segcblist_init(&sp->srcu_cblist);
INIT_DELAYED_WORK(&sp->work, process_srcu); INIT_DELAYED_WORK(&sp->work, process_srcu);
sp->per_cpu_ref = alloc_percpu(struct srcu_array); sp->per_cpu_ref = alloc_percpu(struct srcu_array);
...@@ -180,6 +179,9 @@ static bool srcu_readers_active(struct srcu_struct *sp) ...@@ -180,6 +179,9 @@ static bool srcu_readers_active(struct srcu_struct *sp)
return sum; return sum;
} }
#define SRCU_CALLBACK_BATCH 10
#define SRCU_INTERVAL 1
/** /**
* cleanup_srcu_struct - deconstruct a sleep-RCU structure * cleanup_srcu_struct - deconstruct a sleep-RCU structure
* @sp: structure to clean up. * @sp: structure to clean up.
...@@ -200,8 +202,10 @@ void cleanup_srcu_struct(struct srcu_struct *sp) ...@@ -200,8 +202,10 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist))) if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)))
return; /* Leakage unless caller handles error. */ return; /* Leakage unless caller handles error. */
flush_delayed_work(&sp->work); flush_delayed_work(&sp->work);
if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE)) if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) {
pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
return; /* Caller forgot to stop doing call_srcu()? */ return; /* Caller forgot to stop doing call_srcu()? */
}
free_percpu(sp->per_cpu_ref); free_percpu(sp->per_cpu_ref);
sp->per_cpu_ref = NULL; sp->per_cpu_ref = NULL;
} }
...@@ -253,10 +257,13 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); ...@@ -253,10 +257,13 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
*/ */
static void srcu_gp_start(struct srcu_struct *sp) static void srcu_gp_start(struct srcu_struct *sp)
{ {
int state;
rcu_segcblist_accelerate(&sp->srcu_cblist, rcu_segcblist_accelerate(&sp->srcu_cblist,
rcu_seq_snap(&sp->srcu_gp_seq)); rcu_seq_snap(&sp->srcu_gp_seq));
WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
rcu_seq_start(&sp->srcu_gp_seq); rcu_seq_start(&sp->srcu_gp_seq);
state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
} }
/* /*
...@@ -300,7 +307,6 @@ static void srcu_flip(struct srcu_struct *sp) ...@@ -300,7 +307,6 @@ static void srcu_flip(struct srcu_struct *sp)
static void srcu_gp_end(struct srcu_struct *sp) static void srcu_gp_end(struct srcu_struct *sp)
{ {
rcu_seq_end(&sp->srcu_gp_seq); rcu_seq_end(&sp->srcu_gp_seq);
WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
spin_lock_irq(&sp->queue_lock); spin_lock_irq(&sp->queue_lock);
rcu_segcblist_advance(&sp->srcu_cblist, rcu_segcblist_advance(&sp->srcu_cblist,
...@@ -345,7 +351,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head, ...@@ -345,7 +351,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
spin_lock_irqsave(&sp->queue_lock, flags); spin_lock_irqsave(&sp->queue_lock, flags);
smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */ smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
rcu_segcblist_enqueue(&sp->srcu_cblist, head, false); rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) { if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
srcu_gp_start(sp); srcu_gp_start(sp);
queue_delayed_work(system_power_efficient_wq, &sp->work, 0); queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
} }
...@@ -378,7 +384,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount) ...@@ -378,7 +384,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
head->func = wakeme_after_rcu; head->func = wakeme_after_rcu;
spin_lock_irq(&sp->queue_lock); spin_lock_irq(&sp->queue_lock);
smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */ smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) { if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) {
/* steal the processing owner */ /* steal the processing owner */
rcu_segcblist_enqueue(&sp->srcu_cblist, head, false); rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
srcu_gp_start(sp); srcu_gp_start(sp);
...@@ -480,9 +486,6 @@ unsigned long srcu_batches_completed(struct srcu_struct *sp) ...@@ -480,9 +486,6 @@ unsigned long srcu_batches_completed(struct srcu_struct *sp)
} }
EXPORT_SYMBOL_GPL(srcu_batches_completed); EXPORT_SYMBOL_GPL(srcu_batches_completed);
#define SRCU_CALLBACK_BATCH 10
#define SRCU_INTERVAL 1
/* /*
* Core SRCU state machine. Advance callbacks from ->batch_check0 to * Core SRCU state machine. Advance callbacks from ->batch_check0 to
* ->batch_check1 and then to ->batch_done as readers drain. * ->batch_check1 and then to ->batch_done as readers drain.
...@@ -491,28 +494,40 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount) ...@@ -491,28 +494,40 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
{ {
int idx; int idx;
WARN_ON_ONCE(sp->srcu_state == SRCU_STATE_IDLE);
/* /*
* Because readers might be delayed for an extended period after * Because readers might be delayed for an extended period after
* fetching ->completed for their index, at any point in time there * fetching ->completed for their index, at any point in time there
* might well be readers using both idx=0 and idx=1. We therefore * might well be readers using both idx=0 and idx=1. We therefore
* need to wait for readers to clear from both index values before * need to wait for readers to clear from both index values before
* invoking a callback. * invoking a callback.
*
* The load-acquire ensures that we see the accesses performed
* by the prior grace period.
*/ */
idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */
if (sp->srcu_state == SRCU_STATE_DONE) if (idx == SRCU_STATE_IDLE) {
spin_lock_irq(&sp->queue_lock);
if (rcu_segcblist_empty(&sp->srcu_cblist)) {
spin_unlock_irq(&sp->queue_lock);
return;
}
idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
if (idx == SRCU_STATE_IDLE)
srcu_gp_start(sp); srcu_gp_start(sp);
spin_unlock_irq(&sp->queue_lock);
if (idx != SRCU_STATE_IDLE)
return; /* Someone else started the grace period. */
}
if (sp->srcu_state == SRCU_STATE_SCAN1) { if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
idx = 1 ^ (sp->completed & 1); idx = 1 ^ (sp->completed & 1);
if (!try_check_zero(sp, idx, trycount)) if (!try_check_zero(sp, idx, trycount))
return; /* readers present, retry after SRCU_INTERVAL */ return; /* readers present, retry after SRCU_INTERVAL */
srcu_flip(sp); srcu_flip(sp);
WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2); rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2);
} }
if (sp->srcu_state == SRCU_STATE_SCAN2) { if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN2) {
/* /*
* SRCU read-side critical sections are normally short, * SRCU read-side critical sections are normally short,
...@@ -563,14 +578,14 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp) ...@@ -563,14 +578,14 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay) static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
{ {
bool pending = true; bool pending = true;
int state;
if (rcu_segcblist_empty(&sp->srcu_cblist)) { if (rcu_segcblist_empty(&sp->srcu_cblist)) {
spin_lock_irq(&sp->queue_lock); spin_lock_irq(&sp->queue_lock);
state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
if (rcu_segcblist_empty(&sp->srcu_cblist) && if (rcu_segcblist_empty(&sp->srcu_cblist) &&
READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) { state == SRCU_STATE_IDLE)
WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
pending = false; pending = false;
}
spin_unlock_irq(&sp->queue_lock); spin_unlock_irq(&sp->queue_lock);
} }
......
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