linux-kernel - [PATCH] Fix bug in mm/thrash.c function grab_swap

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Date:	Thu, 10 May 2007 15:58:32 +0300
From:	Mika Kukkonen <mikukkon@...u.homelinux.net>
To:	akpm@...gle.com, ashwin.chaugule@...unite.com
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] Fix 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

Field token_priority is unsigned, so decrementing first and the checking
is not a good plan. Attached patch (compile tested) reverses the order.

Btw, I'm not sure if likely() makes any sense in this new situation.

Signed-off-by: Mika Kukkonen <mikukkon@....fi>

diff --git a/mm/thrash.c b/mm/thrash.c
index 9ef9071..c4c5205 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 >

-
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