[PATCH RFC exit] Sleep at TASK_IDLE when waiting for application core dump

[Paul E. McKenney]

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.  There does not seem to be
any reasonable benefit to getting these splats.

Therefore, change that TASK_UNINTERRUPTIBLE to TASK_IDLE.

Reported-by: Anhad Jai Singh <ffledgling@xxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Chris Mason <clm@xxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>

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();