Bug in mm/thrash.c function grab_swap_token()

Following bug was uncovered by compiling with '-W' flag:

  CC      mm/thrash.o
mm/thrash.c: In function ‘grab_swap_token’:
mm/thrash.c:52: warning: comparison of unsigned expression < 0 is always false

Variable token_priority is unsigned, so decrementing first and then
checking the result does not work; fixed by reversing the test, patch
attached (compile tested only).

I am not sure if likely() makes much sense in this new situation, but
I'll let somebody else to make a decision on that.

Signed-off-by: Mika Kukkonen <mikukkon@iki.fi>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/mm/thrash.c b/mm/thrash.c
index 9ef9071f99bc..c4c5205a9c35 100644
--- a/mm/thrash.c
+++ b/mm/thrash.c
@@ -48,9 +48,8 @@ void grab_swap_token(void)
                 if (current_interval < current->mm->last_interval)
                         current->mm->token_priority++;
                 else {
-                        current->mm->token_priority--;
-                        if (unlikely(current->mm->token_priority < 0))
-                                current->mm->token_priority = 0;
+                        if (likely(current->mm->token_priority > 0))
+                                current->mm->token_priority--;
                 }
                 /* Check if we deserve the token */
                 if (current->mm->token_priority >