linux-kernel - Re: [PATCH v2] block: fix ioc leak in put_io

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Date:	Wed, 14 Mar 2012 06:44:22 +0800
From:	Xiaotian Feng <xtfeng@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Vivek Goyal <vgoyal@...hat.com>, axboe@...nel.dk,
	linux-kernel@...r.kernel.org, Xiaotian Feng <dannyfeng@...cent.com>
Subject: Re: [PATCH v2] block: fix ioc leak in put_io_context

On Tue, Mar 13, 2012 at 11:49 PM, Tejun Heo <tj@...nel.org> wrote:
> On Tue, Mar 13, 2012 at 10:28:20AM -0400, Vivek Goyal wrote:
>> On Tue, Mar 13, 2012 at 01:21:06PM -0400, Xiaotian Feng wrote:
>> > diff --git a/block/blk-ioc.c b/block/blk-ioc.c
>> > index 8b782a6..9690f27 100644
>> > --- a/block/blk-ioc.c
>> > +++ b/block/blk-ioc.c
>> > @@ -145,6 +145,7 @@ static void ioc_release_fn(struct work_struct *work)
>> >  void put_io_context(struct io_context *ioc)
>> >  {
>> >     unsigned long flags;
>> > +   bool free_ioc = false;
>> >
>> >     if (ioc == NULL)
>> >             return;
>> > @@ -159,8 +160,13 @@ void put_io_context(struct io_context *ioc)
>> >             spin_lock_irqsave(&ioc->lock, flags);
>> >             if (!hlist_empty(&ioc->icq_list))
>> >                     schedule_work(&ioc->release_work);
>> > +           else
>> > +                   free_ioc = true;
>
> Calling kmem_cache_free() here directly is probably better.

I did this on my first try, but I got a kernel warning with the
following spin_unlock on ioc->lock :(
We'll hit a use after free bug then...

>
>> >             spin_unlock_irqrestore(&ioc->lock, flags);
>> >     }
>> > +
>> > +   if (free_ioc)
>> > +           kmem_cache_free(iocontext_cachep, ioc);
>> >  }
>> >  EXPORT_SYMBOL(put_io_context);
>>
>> This one looks good to me. Tejun?
>>
>> Acked-by: Vivek Goyal <vgoyal@...hat.com>
>
> Acked-by: Tejun Heo <tj@...nel.org>
>
> Thanks.
>
> --
> tejun
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