Bug in mm/thrash.c function grab_swap_token()
Mika Kukkonen [Fri, 11 May 2007 05:22:17 +0000 (22:22 -0700)]
Following bug was uncovered by compiling with '-W' flag:

CC mm/thrash.o
mm/thrash.c: In function â\200\230grab_swap_tokenâ\200\231:
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>

mm/thrash.c

index 9ef9071..c4c5205 100644 (file)
@@ -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 >