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Message-ID: <21406a91-8801-453a-9833-a4e24c7e90ca@paulmck-laptop>
Date: Thu, 25 Jul 2024 09:24:12 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: linux-kernel@...r.kernel.org, axboe@...nel.dk, brauner@...nel.org,
akpm@...ux-foundation.org, willy@...radead.org, clm@...com,
riel@...riel.com, ffledgling@...a.com
Subject: Re: [PATCH RFC exit] Sleep at TASK_IDLE when waiting for application
core dump
On Thu, Jul 25, 2024 at 03:29:35PM +0200, Oleg Nesterov wrote:
> On 07/24, Paul E. McKenney wrote:
> >
> > Currently, the coredump_task_exit() function sets the task state to
> > TASK_UNINTERRUPTIBLE|TASK_FREEZABLE, which usually works well. But a
> > combination of large memory and slow (and/or highly contended) mass
> > storage can cause application core dumps to take more than two minutes,
> > which can triggers "task blocked" splats.
>
> Do you mean check_hung_uninterruptible_tasks() ?
Yes, from its call to check_hung_task(). Good point, I will add that
to the commit log.
> In any case,
>
> > Therefore, change that TASK_UNINTERRUPTIBLE to TASK_IDLE.
> ...
> > @@ -429,7 +429,7 @@ static void coredump_task_exit(struct task_struct *tsk)
> > complete(&core_state->startup);
> >
> > for (;;) {
> > - set_current_state(TASK_UNINTERRUPTIBLE|TASK_FREEZABLE);
> > + set_current_state(TASK_IDLE|TASK_FREEZABLE);
>
> To me this change makes sense regardless...
>
> To some degree TASK_UNINTERRUPTIBLE is misleading, in that the task which
> sleeps in coredump_task_exit() is _KILLABLE, although not "directly".
>
> A SIGKILL sent to the coredumping process will interrupt the coredumping thread
> (see the signal->core_state check in prepare_signal() and fatal_signal_pending()
> check in dump_interrupted()) and then this thread will wakeup the threads sleeping
> in coredump_task_exit(), see coredump_finish().
Very good, I will add this to the commit log with attribution.
> Acked-by: Oleg Nesterov <oleg@...hat.com>
Thank you for the thorough review! How does the updated patch shown
below look to you?
Thanx, Paul
------------------------------------------------------------------------
commit a6c7779283d67a409b81616a5b485ac21637d7e7
Author: Paul E. McKenney <paulmck@...nel.org>
Date: Wed Jul 24 16:51:52 2024 -0700
exit: Sleep at TASK_IDLE when waiting for application core dump
Currently, the coredump_task_exit() function sets the task state
to TASK_UNINTERRUPTIBLE|TASK_FREEZABLE, which usually works well.
But a combination of large memory and slow (and/or highly contended)
mass storage can cause application core dumps to take more than
two minutes, which can cause check_hung_task(), which is invoked by
check_hung_uninterruptible_tasks(), to produce task-blocked splats.
There does not seem to be any reasonable benefit to getting these splats.
Furthermore, as Oleg Nesterov points out, TASK_UNINTERRUPTIBLE could
be misleading because the task sleeping in coredump_task_exit() really
is killable, albeit indirectly. See the check of signal->core_state
in prepare_signal() and the check of fatal_signal_pending()
in dump_interrupted(), which bypass the normal unkillability of
TASK_UNINTERRUPTIBLE, resulting in coredump_finish() invoking
wake_up_process() on any threads sleeping in coredump_task_exit().
Therefore, change that TASK_UNINTERRUPTIBLE to TASK_IDLE.
Reported-by: Anhad Jai Singh <ffledgling@...a.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: Chris Mason <clm@...com>
Cc: Rik van Riel <riel@...riel.com>
diff --git a/kernel/exit.c b/kernel/exit.c
index f95a2c1338a8..b0d18f7b6d15 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -429,7 +429,7 @@ static void coredump_task_exit(struct task_struct *tsk)
complete(&core_state->startup);
for (;;) {
- set_current_state(TASK_UNINTERRUPTIBLE|TASK_FREEZABLE);
+ set_current_state(TASK_IDLE|TASK_FREEZABLE);
if (!self.task) /* see coredump_finish() */
break;
schedule();
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