With hooks below, we can mark a lock-owned thread with an identifiable flag, which can protect it from being preempted by some other unimportant threads, and then waiter will be wakeup more quickly.
https://android-review.googlesource.com/c/kernel/common/+/2183353
but now we find an issue like this one:
static inline void __up_write(struct rw_semaphore *sem)
{
...
// Step 1. we clear flag.
trace_android_vh_record_rwsem_lock_starttime(current, 0);
// Step 2. owner may be preempted by unimportant threads.
rwsem_clear_owner(sem);
...
// Step 3. wake up waiter, but it's too later.
if (unlikely(tmp & RWSEM_FLAG_WAITERS))
rwsem_wake(sem);
}
This patch will clear protect-flag after waking up waiters.
Bug: 286024926
Change-Id: I71f8b6a7d8a01336fd36b8267c2cb5edab65bd11
Signed-off-by: xieliujie <xieliujie@oppo.com>
xieliujie
403d5d1318