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| author | Oleg Nesterov <oleg@redhat.com> | 2020-02-18 16:50:18 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2020-03-02 14:06:33 -0700 |
| commit | 6fb614920b38bbf3c1c7fcd944c6d9b5d746103d (patch) | |
| tree | 07e72f16b7e06d68a6cdfc915dcf4289e188f2bf /kernel/task_work.c | |
| parent | 3684f24653534c71c7dc9f44d7281a838f4e4979 (diff) | |
| download | lwn-6fb614920b38bbf3c1c7fcd944c6d9b5d746103d.tar.gz lwn-6fb614920b38bbf3c1c7fcd944c6d9b5d746103d.zip | |
task_work_run: don't take ->pi_lock unconditionally
As Peter pointed out, task_work() can avoid ->pi_lock and cmpxchg()
if task->task_works == NULL && !PF_EXITING.
And in fact the only reason why task_work_run() needs ->pi_lock is
the possible race with task_work_cancel(), we can optimize this code
and make the locking more clear.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'kernel/task_work.c')
| -rw-r--r-- | kernel/task_work.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/kernel/task_work.c b/kernel/task_work.c index 0fef395662a6..825f28259a19 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -97,16 +97,26 @@ void task_work_run(void) * work->func() can do task_work_add(), do not set * work_exited unless the list is empty. */ - raw_spin_lock_irq(&task->pi_lock); do { + head = NULL; work = READ_ONCE(task->task_works); - head = !work && (task->flags & PF_EXITING) ? - &work_exited : NULL; + if (!work) { + if (task->flags & PF_EXITING) + head = &work_exited; + else + break; + } } while (cmpxchg(&task->task_works, work, head) != work); - raw_spin_unlock_irq(&task->pi_lock); if (!work) break; + /* + * Synchronize with task_work_cancel(). It can not remove + * the first entry == work, cmpxchg(task_works) must fail. + * But it can remove another entry from the ->next list. + */ + raw_spin_lock_irq(&task->pi_lock); + raw_spin_unlock_irq(&task->pi_lock); do { next = work->next; |