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: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index db023e2ff3852f544c6a4b0f8cb3b43ecd0d456b..56651a10c36645a7f58c87ac9b97599b72255b61 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -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;
@@ -1335,12 +1333,19 @@ static int kswapd(void *p)
                         */
                        order = new_order;
                } else {
-                       schedule();
+                       if (!freezing(current))
+                               schedule();
+
                        order = pgdat->kswapd_max_order;
                }
                finish_wait(&pgdat->kswapd_wait, &wait);
 
-               balance_pgdat(pgdat, order);
+               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;
 }