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locking/rwsem: Add ACQUIRE comments

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Since we just reviewed read_slowpath for ACQUIRE correctness, add a
few coments to retain our findings.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2019-07-18 15:08:53 +02:00 committed by Ingo Molnar
parent 952041a863
commit 6ffddfb9e1
1 changed files with 13 additions and 5 deletions
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18
kernel/locking/rwsem.c
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@ -1004,6 +1004,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
atomic_long_add(-RWSEM_READER_BIAS, &sem->count); atomic_long_add(-RWSEM_READER_BIAS, &sem->count);
adjustment = 0; adjustment = 0;
if (rwsem_optimistic_spin(sem, false)) { if (rwsem_optimistic_spin(sem, false)) {
/* rwsem_optimistic_spin() implies ACQUIRE on success */
/* /*
* Wake up other readers in the wait list if the front * Wake up other readers in the wait list if the front
* waiter is a reader. * waiter is a reader.
@ -1018,6 +1019,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state)
} }
return sem; return sem;
} else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) { } else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) {
/* rwsem_reader_phase_trylock() implies ACQUIRE on success */
return sem; return sem;
} }
@ -1071,10 +1073,10 @@ queue:
wake_up_q(&wake_q); wake_up_q(&wake_q);
/* wait to be given the lock */ /* wait to be given the lock */
while (true) { for (;;) {
set_current_state(state); set_current_state(state);
if (!smp_load_acquire(&waiter.task)) { if (!smp_load_acquire(&waiter.task)) {
/* Orders against rwsem_mark_wake()'s smp_store_release() */ /* Matches rwsem_mark_wake()'s smp_store_release(). */
break; break;
} }
if (signal_pending_state(state, current)) { if (signal_pending_state(state, current)) {
@ -1082,6 +1084,7 @@ queue:
if (waiter.task) if (waiter.task)
goto out_nolock; goto out_nolock;
raw_spin_unlock_irq(&sem->wait_lock); raw_spin_unlock_irq(&sem->wait_lock);
/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
break; break;
} }
schedule(); schedule();
@ -1091,6 +1094,7 @@ queue:
__set_current_state(TASK_RUNNING); __set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock); lockevent_inc(rwsem_rlock);
return sem; return sem;
out_nolock: out_nolock:
list_del(&waiter.list); list_del(&waiter.list);
if (list_empty(&sem->wait_list)) { if (list_empty(&sem->wait_list)) {
@ -1131,8 +1135,10 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
/* do optimistic spinning and steal lock if possible */ /* do optimistic spinning and steal lock if possible */
if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) && if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) &&
rwsem_optimistic_spin(sem, true)) rwsem_optimistic_spin(sem, true)) {
/* rwsem_optimistic_spin() implies ACQUIRE on success */
return sem; return sem;
}
/* /*
* Disable reader optimistic spinning for this rwsem after * Disable reader optimistic spinning for this rwsem after
@ -1192,9 +1198,11 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
wait: wait:
/* wait until we successfully acquire the lock */ /* wait until we successfully acquire the lock */
set_current_state(state); set_current_state(state);
while (true) { for (;;) {
if (rwsem_try_write_lock(sem, wstate)) if (rwsem_try_write_lock(sem, wstate)) {
/* rwsem_try_write_lock() implies ACQUIRE on success */
break; break;
}
raw_spin_unlock_irq(&sem->wait_lock); raw_spin_unlock_irq(&sem->wait_lock);