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authorPeter Zijlstra <peterz@infradead.org>2021-09-09 12:59:18 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-09-15 17:49:15 +0200
commit616be87eac9fa2ab2dca1069712f7236e50f3bf6 (patch)
tree0f2ddfc328c5bdd742604e2c2fe14f3926d82dd7 /kernel/locking
parent7687201e37fabf2b7cf2b828f7ca46bf30e2948f (diff)
locking/rwbase: Extract __rwbase_write_trylock()
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
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rwbase_rt.c44
1 files changed, 26 insertions, 18 deletions
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 542b0170e4f5..48fbbccdce3f 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -196,6 +196,19 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb)
__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,
unsigned int state)
{
@@ -210,34 +223,30 @@ static int __sched rwbase_write_lock(struct rwbase_rt *rwb,
atomic_sub(READER_BIAS, &rwb->readers);
raw_spin_lock_irqsave(&rtm->wait_lock, flags);
- /*
- * set_current_state() for rw_semaphore
- * current_save_and_set_rtlock_wait_state() for rwlock
- */
- rwbase_set_and_save_current_state(state);
+ if (__rwbase_write_trylock(rwb))
+ goto out_unlock;
- /* Block until all readers have left the critical section. */
- for (; atomic_read(&rwb->readers);) {
+ rwbase_set_and_save_current_state(state);
+ for (;;) {
/* Optimized out for rwlocks */
if (rwbase_signal_pending_state(state, current)) {
rwbase_restore_current_state();
__rwbase_write_unlock(rwb, 0, flags);
return -EINTR;
}
+
+ if (__rwbase_write_trylock(rwb))
+ break;
+
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
+ rwbase_schedule();
+ raw_spin_lock_irqsave(&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();
set_current_state(state);
- raw_spin_lock_irqsave(&rtm->wait_lock, flags);
}
-
- atomic_set(&rwb->readers, WRITER_BIAS);
rwbase_restore_current_state();
+
+out_unlock:
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
return 0;
}
@@ -253,8 +262,7 @@ static inline int rwbase_write_trylock(struct rwbase_rt *rwb)
atomic_sub(READER_BIAS, &rwb->readers);
raw_spin_lock_irqsave(&rtm->wait_lock, flags);
- if (!atomic_read(&rwb->readers)) {
- atomic_set(&rwb->readers, WRITER_BIAS);
+ if (__rwbase_write_trylock(rwb)) {
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
return 1;
}