Messages in this thread Patch in this message | | | From | Kamal Mostafa <> | Subject | [PATCH 4.2.y-ckt 015/211] task_work: remove fifo ordering guarantee | Date | Tue, 5 Jan 2016 11:42:03 -0800 |
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4.2.8-ckt1 -stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet <edumazet@google.com>
commit c82199061009d1561e31e17fca5e47a87cb7ff4c upstream.
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 <edumazet@google.com> Reported-by: Maciej Żenczykowski <maze@google.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- kernel/task_work.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-)
diff --git a/kernel/task_work.c b/kernel/task_work.c index 8727032..53fa971 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); -- 1.9.1
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