linux-kernel - Re: [Slub allocator] There are chances that kmem_cache_cpu->freelist gets lost if the process happens to be rescheduled to a differenet cpu before the local_irq_save() completes in __slab

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Date:	Mon, 12 Dec 2011 18:39:18 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	zhihua che <zhihua.che@...il.com>, linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [Slub allocator] There are chances that
 kmem_cache_cpu->freelist gets lost if the process happens to be rescheduled
 to a differenet cpu before the local_irq_save() completes in __slab_alloc()

Le lundi 12 décembre 2011 à 09:50 -0600, Christoph Lameter a écrit :

> Correct. Issue was introduced in 2.6.39.
> 
> Acked-by: Christoph Lameter <cl@...ux.com>
> 

Indeed, I reproduced the leak with hackbench and lot of threads.

Thanks

[PATCH] slub: fix a possible memleak in __slab_alloc()

Zhihua Che reported a possible memleak in slub allocator on
CONFIG_PREEMPT=y builds.

It is possible current thread migrates right before disabling irqs in
__slab_alloc(). We must check again c->freelist, and perform a normal
allocation instead of scratching c->freelist.

Many thanks to Zhihua Che for spotting this bug, introduced in 2.6.39

Reported-by: zhihua che <zhihua.che@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Acked-by: Christoph Lameter <cl@...ux.com>
CC: Pekka Enberg <penberg@...helsinki.fi>
CC: stable@...r.kernel.org
---
 mm/slub.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index ed3334d..923d238 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2166,6 +2166,12 @@ redo:
 		goto new_slab;
 	}
 
+#ifdef CONFIG_PREEMPT
+	object = c->freelist;
+	if (object)
+		goto load_freelist;
+#endif
+
 	stat(s, ALLOC_SLOWPATH);
 
 	do {


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