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:	Tue, 13 Dec 2011 12:47:06 +0800
From:	zhihua che <zhihua.che@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Christoph Lameter <cl@...ux.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()

2011/12/13 Eric Dumazet <eric.dumazet@...il.com>:
> Le lundi 12 décembre 2011 à 18:39 +0100, Eric Dumazet a écrit :
>> 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 {
>>
>
> Thinking again about the issue, I believe its not a CONFIG_PREEMPT only
> one.
>
> We can be interrupted and the IRQ handler can free an object an populate
> freelist too. So the check must always be done.
>
> Thanks
>
> [PATCH v2] 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
>
> V2: Its also possible an IRQ freed one (or several) object(s) and
> populated c->freelist, so its not a CONFIG_PREEMPT only problem.
>
> Reported-by: zhihua che <zhihua.che@...il.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> CC: Christoph Lameter <cl@...ux.com>
> CC: Pekka Enberg <penberg@...helsinki.fi>
> ---
>  mm/slub.c |    5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index ed3334d..1a919f0 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2166,6 +2166,11 @@ redo:
>                goto new_slab;
>        }
>
> +       /* must check again c->freelist in case of cpu migration or IRQ */
> +       object = c->freelist;
> +       if (object)
> +               goto load_freelist;
> +
>        stat(s, ALLOC_SLOWPATH);
>
>        do {
>
>

I'm glad and excited I can help. :-)
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