Re: cgroup/loop Bad page state oops in Linux v4.2-rc3-136-g45b4b782e848

[Mike Snitzer]

On Sun, Aug 02 2015 at 10:01P -0400,
Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> wrote:

> On Fri, Jul 31, 2015 at 2:58 PM, Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> wrote:
> > On Thu, Jul 30, 2015 at 8:19 PM, Mike Snitzer <snitzer@xxxxxxxxxx> 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)?

Thanks.

From: Mike Snitzer <snitzer@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxx>
Acked-by: Joe Thornber <ejt@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 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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