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| author | Waiman Long <longman@redhat.com> | 2019-05-20 22:59:07 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-06-17 12:28:00 +0200 |
| commit | 00f3c5a3df2c1e3dab14d0dd2b71f852d46be97f (patch) | |
| tree | e2a43358ed69c8cab7b5801552797cdd61d69b44 /include | |
| parent | locking/rwsem: Implement lock handoff to prevent lock starvation (diff) | |
| download | linux-00f3c5a3df2c1e3dab14d0dd2b71f852d46be97f.tar.xz linux-00f3c5a3df2c1e3dab14d0dd2b71f852d46be97f.zip | |
locking/rwsem: Always release wait_lock before waking up tasks
With the use of wake_q, we can do task wakeups without holding the
wait_lock. There is one exception in the rwsem code, though. It is
when the writer in the slowpath detects that there are waiters ahead
but the rwsem is not held by a writer. This can lead to a long wait_lock
hold time especially when a large number of readers are to be woken up.
Remediate this situation by releasing the wait_lock before waking
up tasks and re-acquiring it afterward. The rwsem_try_write_lock()
function is also modified to read the rwsem count directly to avoid
stale count value.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-9-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/sched/wake_q.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/sched/wake_q.h b/include/linux/sched/wake_q.h index ad826d2a4557..26a2013ac39c 100644 --- a/include/linux/sched/wake_q.h +++ b/include/linux/sched/wake_q.h @@ -51,6 +51,11 @@ static inline void wake_q_init(struct wake_q_head *head) head->lastp = &head->first; } +static inline bool wake_q_empty(struct wake_q_head *head) +{ + return head->first == WAKE_Q_TAIL; +} + extern void wake_q_add(struct wake_q_head *head, struct task_struct *task); extern void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task); extern void wake_up_q(struct wake_q_head *head); |