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 <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>
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 @@
* 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 @@
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);
