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locking/rwbase: Extract __rwbase_write_trylock()

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The code in rwbase_write_lock() is a little non-obvious vs the
read+set 'trylock', extract the sequence into a helper function to
clarify the code.

This also provides a single site to fix fast-path ordering.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/YUCq3L+u44NDieEJ@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2021-09-09 12:59:18 +02:00
parent 7687201e37
commit 616be87eac
1 changed files with 27 additions and 19 deletions
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44
kernel/locking/rwbase_rt.c
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@ -196,6 +196,19 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb)
__rwbase_write_unlock(rwb, WRITER_BIAS - 1, flags); __rwbase_write_unlock(rwb, WRITER_BIAS - 1, flags);
} }
static inline bool __rwbase_write_trylock(struct rwbase_rt *rwb)
{
/* Can do without CAS because we're serialized by wait_lock. */
lockdep_assert_held(&rwb->rtmutex.wait_lock);
if (!atomic_read(&rwb->readers)) {
atomic_set(&rwb->readers, WRITER_BIAS);
return 1;
}
return 0;
}
static int __sched rwbase_write_lock(struct rwbase_rt *rwb, static int __sched rwbase_write_lock(struct rwbase_rt *rwb,
unsigned int state) unsigned int state)
{ {
@ -210,34 +223,30 @@ static int __sched rwbase_write_lock(struct rwbase_rt *rwb,
atomic_sub(READER_BIAS, &rwb->readers); atomic_sub(READER_BIAS, &rwb->readers);
raw_spin_lock_irqsave(&rtm->wait_lock, flags); raw_spin_lock_irqsave(&rtm->wait_lock, flags);
/* if (__rwbase_write_trylock(rwb))
* set_current_state() for rw_semaphore goto out_unlock;
* current_save_and_set_rtlock_wait_state() for rwlock
*/
rwbase_set_and_save_current_state(state);
/* Block until all readers have left the critical section. */ rwbase_set_and_save_current_state(state);
for (; atomic_read(&rwb->readers);) { for (;;) {
/* Optimized out for rwlocks */ /* Optimized out for rwlocks */
if (rwbase_signal_pending_state(state, current)) { if (rwbase_signal_pending_state(state, current)) {
rwbase_restore_current_state(); rwbase_restore_current_state();
__rwbase_write_unlock(rwb, 0, flags); __rwbase_write_unlock(rwb, 0, flags);
return -EINTR; return -EINTR;
} }
if (__rwbase_write_trylock(rwb))
break;
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags); raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
/*
* Schedule and wait for the readers to leave the critical
* section. The last reader leaving it wakes the waiter.
*/
if (atomic_read(&rwb->readers) != 0)
rwbase_schedule(); rwbase_schedule();
set_current_state(state);
raw_spin_lock_irqsave(&rtm->wait_lock, flags); raw_spin_lock_irqsave(&rtm->wait_lock, flags);
}
atomic_set(&rwb->readers, WRITER_BIAS); set_current_state(state);
}
rwbase_restore_current_state(); rwbase_restore_current_state();
out_unlock:
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags); raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
return 0; return 0;
} }
@ -253,8 +262,7 @@ static inline int rwbase_write_trylock(struct rwbase_rt *rwb)
atomic_sub(READER_BIAS, &rwb->readers); atomic_sub(READER_BIAS, &rwb->readers);
raw_spin_lock_irqsave(&rtm->wait_lock, flags); raw_spin_lock_irqsave(&rtm->wait_lock, flags);
if (!atomic_read(&rwb->readers)) { if (__rwbase_write_trylock(rwb)) {
atomic_set(&rwb->readers, WRITER_BIAS);
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags); raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
return 1; return 1;
} }