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>

1 files changed, 9 insertions, 4 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index db023e2ff385..56651a10c366 100644
--- 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;
 }