linux-kernel - [PATCH 30/31] Fix use of uninitialized variable in cache

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Message-Id: <1254406257-16735-1-git-send-email-sjayaraman@suse.de>
Date:	Thu,  1 Oct 2009 19:40:57 +0530
From:	Suresh Jayaraman <sjayaraman@...e.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	netdev@...r.kernel.org, Neil Brown <neilb@...e.de>,
	Miklos Szeredi <mszeredi@...e.cz>, Wouter Verhelst <w@...r.be>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	trond.myklebust@....uio.no, Suresh Jayaraman <sjayaraman@...e.de>
Subject: [PATCH 30/31] Fix use of uninitialized variable in cache_grow()

From: Miklos Szeredi <mszeredi@...e.cz>

This fixes a bug in reserve-slub.patch.

If cache_grow() was called with objp != NULL then the 'reserve' local
variable wasn't initialized. This resulted in ac->reserve being set to
a rubbish value.  Due to this in some circumstances huge amounts of
slab pages were allocated (due to slab_force_alloc() returning true),
which caused atomic page allocation failures and slowdown of the
system.

Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
Signed-off-by: Suresh Jayaraman <sjayaraman@...e.de>
---
 mm/slab.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Index: mmotm/mm/slab.c
===================================================================
--- mmotm.orig/mm/slab.c
+++ mmotm/mm/slab.c
@@ -2760,7 +2760,7 @@ static int cache_grow(struct kmem_cache
 	size_t offset;
 	gfp_t local_flags;
 	struct kmem_list3 *l3;
-	int reserve;
+	int reserve = -1;
 
 	/*
 	 * Be lazy and only check for valid flags here,  keeping it out of the
@@ -2816,7 +2816,8 @@ static int cache_grow(struct kmem_cache
 	if (local_flags & __GFP_WAIT)
 		local_irq_disable();
 	check_irq_off();
-	slab_set_reserve(cachep, reserve);
+	if (reserve != -1)
+		slab_set_reserve(cachep, reserve);
 	spin_lock(&l3->list_lock);
 
 	/* Make slab active. */
--
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