Date: Tue, 25 Nov 2014 20:00:08 -0800
From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Mike Snitzer <snitzer@redhat.com>
Cc: device-mapper development <dm-devel@redhat.com>,
        linux-kernel@vger.kernel.org, Alasdair Kergon <agk@redhat.com>
Subject: Re: [dm-devel] dm-bufio: fix memleak when using a dm_buffer's inline
 bio
Message-ID: <20141126040008.GF10050@birch.djwong.org>
References: <20141126014515.GE10050@birch.djwong.org>
 <20141126034103.GA26585@redhat.com>
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On Tue, Nov 25, 2014 at 10:41:04PM -0500, Mike Snitzer wrote:
> On Tue, Nov 25 2014 at  8:45pm -0500,
> Darrick J. Wong <darrick.wong@oracle.com> wrote:
> 
> > When dm-bufio sets out to use the bio built into a struct dm_buffer to
> > issue an IO, it needs to call bio_reset after it's done with the bio
> > so that we can free things attached to the bio such as the integrity
> > payload.  Therefore, inject our own endio callback to take care of
> > the bio_reset after calling submit_io's end_io callback.
> > 
> > Test case:
> > 1. modprobe scsi_debug delay=0 dif=1 dix=199 ato=1 dev_size_mb=300
> > 2. Set up a dm-bufio client, e.g. dm-verity, on the scsi_debug device
> > 3. Repeatedly read metadata and watch kmalloc-192 leak!
> > 
> > Fix is against 3.18-rc6.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Thanks for reporting/fixing this.
> 
> Alternatively I think we could just call bio_reset() in submit_io(),
> e.g.:
> 
> diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
> index afe7971..e7036e3 100644
> --- a/drivers/md/dm-bufio.c
> +++ b/drivers/md/dm-bufio.c
> @@ -579,6 +579,8 @@ static void submit_io(struct dm_buffer *b, int rw, sector_t block,
>  	if (rw == WRITE && b->c->write_callback)
>  		b->c->write_callback(b);
>  
> +	bio_reset(&b->bio);
> +
>  	if (b->c->block_size <= DM_BUFIO_INLINE_VECS * PAGE_SIZE &&
>  	    b->data_mode != DATA_MODE_VMALLOC)
>  		use_inline_bio(b, rw, block, end_io);
> 
> What do you think?

I decided to call bio_reset after calling end_io so that we can free
the integrity buffer as soon as we're done with the bio.  Calling
bio_reset just prior to the next submit_bio as this snippet does means
that the integrity buffer remains attached to the bio until just
before the next submit_bio call, which could be a while.

Also, I think use_dmio results in a new bio being used instead of the
bio embedded in the dm_buffer, so it shouldn't be necessary to reset
the bio if the previous IO had use_dmio'd.

--D

> 
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