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Commit b1296cc4 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki Committed by Linus Torvalds
Browse files

freezer: fix racy usage of try_to_freeze in kswapd 



Currently we can miss freeze_process()->signal_wake_up() in kswapd() if it
happens between try_to_freeze() and prepare_to_wait().  To prevent this
from happening we should check freezing(current) before calling schedule().

Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d1d241cc

mm/vmscan.c

+9 −4
Original line number Diff line number Diff line
@@ -1323,8 +1323,6 @@ static int kswapd(void *p) 
	for ( ; ; ) {

		unsigned long new_order;



		try_to_freeze();



		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);

		new_order = pgdat->kswapd_max_order;

		pgdat->kswapd_max_order = 0;
@@ -1335,13 +1333,20 @@ static int kswapd(void *p) 
			 */

			order = new_order;

		} else {

			if (!freezing(current))

				schedule();



			order = pgdat->kswapd_max_order;

		}

		finish_wait(&pgdat->kswapd_wait, &wait);



		if (!try_to_freeze()) {

			/* We can speed up thawing tasks if we don't call

			 * balance_pgdat after returning from the refrigerator

			 */

			balance_pgdat(pgdat, order);

		}

	}

	return 0;

}