In percpu reader mode, trylock() for read had a lost wakeup: on failure
to get the lock, we may have caused a writer to fail to get the lock,
because we temporarily elevated the reader count.
We need to check for waiters after decrementing the read count - not
before.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
this_cpu_sub(*lock->readers, !ret);
preempt_enable();
- if (!ret && (old & SIX_LOCK_WAITING_write))
- ret = -1 - SIX_LOCK_write;
+ if (!ret) {
+ smp_mb();
+ if (atomic_read(&lock->state) & SIX_LOCK_WAITING_write)
+ ret = -1 - SIX_LOCK_write;
+ }
} else if (type == SIX_LOCK_write && lock->readers) {
if (try) {
atomic_add(SIX_LOCK_HELD_write, &lock->state);