Jens Axboe ebf0d100df
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 >
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