Date:	Mon, 3 Aug 2015 12:56:29 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	ejt@...hat.com, Ming Lei <ming.lei@...onical.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...com>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: cgroup/loop Bad page state oops in Linux v4.2-rc3-136-g45b4b782e848

On Mon, Aug 3, 2015 at 10:28 AM, Mike Snitzer <snitzer@...hat.com> wrote:
> On Sun, Aug 02 2015 at 10:01P -0400,
> Josh Boyer <jwboyer@...oraproject.org> wrote:
>
>> On Fri, Jul 31, 2015 at 2:58 PM, Josh Boyer <jwboyer@...oraproject.org> wrote:
>> > On Thu, Jul 30, 2015 at 8:19 PM, Mike Snitzer <snitzer@...hat.com> wrote:
>> >>
>> >> The only commit that looks even remotely related (given 32bit concerns)
>> >> would be 1c220c69ce0dcc0f234a9f263ad9c0864f971852
>> >
>> > Confirmed.  I built kernels for our tester that started with the
>> > working snapshot and applied the patches above one at a time.  The
>> > failing patch was the commit you suspected.
>> >
>> > I can try and build a 4.2-rc4 kernel with that reverted, but it would
>> > be good if someone could start thinking about how that could cause
>> > this issue.
>>
>> A revert on top of 4.2-rc4 booted.  So this is currently causing
>> issues with upstream as well.
>
> Hi Josh,
>
> I've staged the following fix in linux-next (for 4.2-rc6 inclusion):
> https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=76270d574acc897178a5c8be0bd2a743a77e4bac
>
> Can you please verify that it works for your 32bit testcase against
> 4.2-rc4 (or rc5)?

Sure, I'll get a kernel with this included spun up and ask Adam to test.

josh

> From: Mike Snitzer <snitzer@...hat.com>
> Date: Mon, 3 Aug 2015 09:54:58 -0400
> Subject: [PATCH] dm: fix dm_merge_bvec regression on 32 bit systems
>
> A DM regression on 32 bit systems was reported against v4.2-rc3 here:
> https://lkml.org/lkml/2015/7/29/401
>
> Fix this by reverting both commit 1c220c69 ("dm: fix casting bug in
> dm_merge_bvec()") and 148e51ba ("dm: improve documentation and code
> clarity in dm_merge_bvec").  This combined revert is done to eliminate
> the possibility of a partial revert in stable@ kernels.
>
> In hindsight the correct fix, at the time 1c220c69 was applied to fix
> the regression that 148e51ba introduced, should've been to simply revert
> 148e51ba.
>
> Reported-by: Josh Boyer <jwboyer@...oraproject.org>
> Acked-by: Joe Thornber <ejt@...hat.com>
> Signed-off-by: Mike Snitzer <snitzer@...hat.com>
> Cc: stable@...r.kernel.org # 3.19+
> ---
>  drivers/md/dm.c | 27 ++++++++++-----------------
>  1 file changed, 10 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index ab37ae1..0d7ab20 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1729,7 +1729,8 @@ static int dm_merge_bvec(struct request_queue *q,
>         struct mapped_device *md = q->queuedata;
>         struct dm_table *map = dm_get_live_table_fast(md);
>         struct dm_target *ti;
> -       sector_t max_sectors, max_size = 0;
> +       sector_t max_sectors;
> +       int max_size = 0;
>
>         if (unlikely(!map))
>                 goto out;
> @@ -1742,18 +1743,10 @@ static int dm_merge_bvec(struct request_queue *q,
>          * Find maximum amount of I/O that won't need splitting
>          */
>         max_sectors = min(max_io_len(bvm->bi_sector, ti),
> -                         (sector_t) queue_max_sectors(q));
> +                         (sector_t) BIO_MAX_SECTORS);
>         max_size = (max_sectors << SECTOR_SHIFT) - bvm->bi_size;
> -
> -       /*
> -        * FIXME: this stop-gap fix _must_ be cleaned up (by passing a sector_t
> -        * to the targets' merge function since it holds sectors not bytes).
> -        * Just doing this as an interim fix for stable@ because the more
> -        * comprehensive cleanup of switching to sector_t will impact every
> -        * DM target that implements a ->merge hook.
> -        */
> -       if (max_size > INT_MAX)
> -               max_size = INT_MAX;
> +       if (max_size < 0)
> +               max_size = 0;
>
>         /*
>          * merge_bvec_fn() returns number of bytes
> @@ -1761,13 +1754,13 @@ static int dm_merge_bvec(struct request_queue *q,
>          * max is precomputed maximal io size
>          */
>         if (max_size && ti->type->merge)
> -               max_size = ti->type->merge(ti, bvm, biovec, (int) max_size);
> +               max_size = ti->type->merge(ti, bvm, biovec, max_size);
>         /*
>          * If the target doesn't support merge method and some of the devices
> -        * provided their merge_bvec method (we know this by looking for the
> -        * max_hw_sectors that dm_set_device_limits may set), then we can't
> -        * allow bios with multiple vector entries.  So always set max_size
> -        * to 0, and the code below allows just one page.
> +        * provided their merge_bvec method (we know this by looking at
> +        * queue_max_hw_sectors), then we can't allow bios with multiple vector
> +        * entries.  So always set max_size to 0, and the code below allows
> +        * just one page.
>          */
>         else if (queue_max_hw_sectors(q) <= PAGE_SIZE >> 9)
>                 max_size = 0;
> --
> 2.3.2 (Apple Git-55)
>
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