diff options
| author | Jens Axboe <axboe@kernel.dk> | 2020-08-13 09:01:38 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2020-08-13 09:01:38 -0600 |
| commit | ebf0d100df0731901c16632f78d78d35f4123bc4 (patch) | |
| tree | 75defc3ec0621de7306f54a658c8797b34cab263 /kernel/task_work.c | |
| parent | f254ac04c8744cf7bfed012717eac34eacc65dfb (diff) | |
task_work: only grab task signal lock when needed
If JOBCTL_TASK_WORK is already set on the targeted task, then we need
not go through {lock,unlock}_task_sighand() to set it again and queue
a signal wakeup. This is safe as we're checking it _after_ adding the
new task_work with cmpxchg().
The ordering is as follows:
task_work_add() get_signal()
--------------------------------------------------------------
STORE(task->task_works, new_work); STORE(task->jobctl);
mb(); mb();
LOAD(task->jobctl); LOAD(task->task_works);
This speeds up TWA_SIGNAL handling quite a bit, which is important now
that io_uring is relying on it for all task_work deliveries.
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jann Horn <jannh@google.com>
Acked-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 | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/task_work.c b/kernel/task_work.c index 5c0848ca1287..613b2d634af8 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -42,7 +42,13 @@ task_work_add(struct task_struct *task, struct callback_head *work, int notify) set_notify_resume(task); break; case TWA_SIGNAL: - if (lock_task_sighand(task, &flags)) { + /* + * Only grab the sighand lock if we don't already have some + * task_work pending. This pairs with the smp_store_mb() + * in get_signal(), see comment there. + */ + if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) && + lock_task_sighand(task, &flags)) { task->jobctl |= JOBCTL_TASK_WORK; signal_wake_up(task, 0); unlock_task_sighand(task, &flags); |