From: Eric Dumazet Date: Sat, 29 Aug 2015 02:42:30 +0000 (-0700) Subject: task_work: remove fifo ordering guarantee X-Git-Tag: Ubuntu-5.0.0-8.9~8749 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=c82199061009d1561e31e17fca5e47a87cb7ff4c;p=mirror_ubuntu-disco-kernel.git task_work: remove fifo ordering guarantee In commit f341861fb0b ("task_work: add a scheduling point in task_work_run()") I fixed a latency problem adding a cond_resched() call. Later, commit ac3d0da8f329 added yet another loop to reverse a list, bringing back the latency spike : I've seen in some cases this loop taking 275 ms, if for example a process with 2,000,000 files is killed. We could add yet another cond_resched() in the reverse loop, or we can simply remove the reversal, as I do not think anything would depend on order of task_work_add() submitted works. Fixes: ac3d0da8f329 ("task_work: Make task_work_add() lockless") Signed-off-by: Eric Dumazet Reported-by: Maciej Żenczykowski Acked-by: Al Viro Signed-off-by: Linus Torvalds --- diff --git a/kernel/task_work.c b/kernel/task_work.c index 8727032e3a6f..53fa971d000d 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -18,6 +18,8 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */ * This is like the signal handler which runs in kernel mode, but it doesn't * try to wake up the @task. * + * Note: there is no ordering guarantee on works queued here. + * * RETURNS: * 0 if succeeds or -ESRCH. */ @@ -108,16 +110,6 @@ void task_work_run(void) raw_spin_unlock_wait(&task->pi_lock); smp_mb(); - /* Reverse the list to run the works in fifo order */ - head = NULL; - do { - next = work->next; - work->next = head; - head = work; - work = next; - } while (work); - - work = head; do { next = work->next; work->func(work);