linux-kernel - Re: [block:for-3.14/core] kernel BUG at fs/bio.c:1748

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Date:	Mon, 6 Jan 2014 16:47:38 -0800
From:	Muthu Kumar <muthu.lkml@...il.com>
To:	Kent Overstreet <kmo@...erainc.com>
Cc:	Chris Mason <clm@...com>, Fengguang Wu <fengguang.wu@...el.com>,
	Jens Axboe <axboe@...nel.dk>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...ux.intel.com
Subject: Re: [block:for-3.14/core] kernel BUG at fs/bio.c:1748

OK, after a bit more staring I believe the correct fix is the following.

Fengguang, Please try this one?

Regards,
Muthu

------------
In btrfs_end_bio(), we increment bi_remaining if is_orig_bio. If not,
we restore the orig_bio but failed to increment bi_remaining for
orig_bio, which triggers a BUG_ON later when bio_endio is called. Fix
is to increment bi_remaining when we restore the orig bio as well.

Reported-by: fengguang.wu@...el.com
CC: Kent Overstreet <kmo@...erainc.com>
CC: Jens Axboe <axboe@...nel.dk>
CC: Chris Mason <clm@fv
Signed-off-by: Muthukumar Ratty <muthur@...il.com>
----------------
 fs/btrfs/volumes.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 37972d5..2011cc0 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5297,9 +5297,9 @@ static void btrfs_end_bio(struct bio *bio, int err)
                if (!is_orig_bio) {
                        bio_put(bio);
                        bio = bbio->orig_bio;
-               } else {
-                       atomic_inc(&bio->bi_remaining);
                }
+               atomic_inc(&bio->bi_remaining);
+
                bio->bi_private = bbio->private;
                bio->bi_end_io = bbio->end_io;
                btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;

--------------------------



On Mon, Jan 6, 2014 at 2:10 PM, Kent Overstreet <kmo@...erainc.com> wrote:
> Chris, the patch below seems to be incorrect - with it we get hangs, so
> bi_remaining (probably) isn't getting decremented when it should be. You sent
> Jens fixes for btrfs which I somehow lost when I rebased, do you remember how
> this is supposed to work? Looking at the code I'm not quite sure what's going on
> here.
>
> On Fri, Jan 03, 2014 at 11:51:31AM -0800, Muthu Kumar wrote:
>> Looks like Kent missed the btrfs endio in the original commit. How
>> about this patch:
>>
>> ---------
>>
>> In btrfs_end_bio, call bio_endio_nodec on the restored bio so the
>> bi_remaining is accounted for correctly.
>>
>> Reported-by: fengguang.wu@...el.com
>> Cc: Kent Overstreet <kmo@...erainc.com>
>> CC: Jens Axboe <axboe@...nel.dk>
>> Signed-off-by: Muthukumar Ratty <muthur@...il.com>
>> --------
>>
>>  fs/btrfs/volumes.c |    6 +++++-
>>  1 files changed, 5 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index f2130de..edfed52 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -5316,7 +5316,11 @@ static void btrfs_end_bio(struct bio *bio, int err)
>>                 }
>>                 kfree(bbio);
>>
>> -               bio_endio(bio, err);
>> +                /*
>> +                 * Call endio_nodec on the restored bio so the bi_remaining is
>> +                 * accounted for correctly
>> +                 */
>> +               bio_endio_nodec(bio, err);
>>         } else if (!is_orig_bio) {
>>                 bio_put(bio);
>>         }
--
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