linux-kernel - [PATCH - V2] Fix missing of last user while dumping slab corruption log

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Date:	Mon, 12 Apr 2010 13:50:56 +0800
From:	ShiYong LI <a22381@...orola.com>
To:	linux-kernel@...r.kernel.org
Cc:	Pekka Enberg <penberg@...helsinki.fi>, cl@...ux-foundation.org,
	mpm@...enic.com, linux-mm@...ck.org, dwmw2@...radead.org,
	TAO HU <taohu@...orola.com>
Subject: [PATCH - V2] Fix missing of last user while dumping slab corruption 
	log

Hi,

Compared to previous version, add alignment checking to make sure
memory space storing redzone2 and last user tags is 8 byte alignment.

>From 949e8c29e8681a2359e23a8fbd8b9d4833f42344 Mon Sep 17 00:00:00 2001
From: Shiyong Li <shi-yong.li@...orola.com>
Date: Mon, 12 Apr 2010 13:48:21 +0800
Subject: [PATCH] Fix missing of last user info while getting
DEBUG_SLAB config enabled.

Even with SLAB_RED_ZONE and SLAB_STORE_USER enabled, kernel would NOT
store redzone and last user data around allocated memory space if arch
cache line > sizeof(unsigned long long). As a result, last user information
is unexpectedly MISSED while dumping slab corruption log.

This fix makes sure that redzone and last user tags get stored unless
the required alignment breaks redzone's.

Signed-off-by: Shiyong Li <shi-yong.li@...orola.com>
---
 mm/slab.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index a8a38ca..b97c57e 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2267,8 +2267,8 @@ kmem_cache_create (const char *name, size_t
size, size_t align,
 	if (ralign < align) {
 		ralign = align;
 	}
-	/* disable debug if necessary */
-	if (ralign > __alignof__(unsigned long long))
+	/* disable debug if not aligning with REDZONE_ALIGN */
+	if (ralign & (__alignof__(unsigned long long) - 1))
 		flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
 	/*
 	 * 4) Store it.
@@ -2289,8 +2289,8 @@ kmem_cache_create (const char *name, size_t
size, size_t align,
 	 */
 	if (flags & SLAB_RED_ZONE) {
 		/* add space for red zone words */
-		cachep->obj_offset += sizeof(unsigned long long);
-		size += 2 * sizeof(unsigned long long);
+		cachep->obj_offset += align;
+		size += align + sizeof(unsigned long long);
 	}
 	if (flags & SLAB_STORE_USER) {
 		/* user store requires one word storage behind the end of
-- 
1.6.0.4





-- 
Thanks & Best Regards
Shiyong
--
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