linux-kernel - [PATCH misc 2/2] exit: Sleep at TASK_IDLE when waiting for application core dump

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Message-Id: <20240802003046.4134043-2-paulmck@kernel.org>
Date: Thu,  1 Aug 2024 17:30:46 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Breno Leitao <leitao@...ian.org>,
	Rik van Riel <riel@...riel.com>,
	Anhad Jai Singh <ffledgling@...a.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Jens Axboe <axboe@...nel.dk>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Chris Mason <clm@...com>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH misc 2/2] 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>
---
 kernel/exit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 7430852a85712..0d62a53605dfc 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -428,7 +428,7 @@ 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();
-- 
2.40.1