Subject: Re: bio linked list corruption.
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Jones <davej@codemonkey.org.uk>, Chris Mason <clm@fb.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
        Josef Bacik <jbacik@fb.com>, David Sterba <dsterba@suse.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Dave Chinner <david@fromorbit.com>
References: <20161026002752.qvrm6yxqb54fiqnd@codemonkey.org.uk>
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 <20161026163018.wx57yy554576s6e2@codemonkey.org.uk>
 <CA+55aFzsrRenu3NsDYr3qqO=fC9FUxkLc3M2wzeLBpN7ghwvwA@mail.gmail.com>
 <20161026184201.6ofblkd3j5uxystq@codemonkey.org.uk>
 <CA+55aFwD9McVapb0svQrrvP1k6iSkqz5ENNGXY6b+Yo-k7wOsg@mail.gmail.com>
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 <CA+55aFwY5jNcUAJzDWERP2r9iZHEKzHSwMi5AJCJiaVd3Z0E-g@mail.gmail.com>
 <20161026224025.mou27kki4bslftli@codemonkey.org.uk>
 <CA+55aFyyP6VHOv6KbhVdMMtNfJLftbju_Ui2GNxXt0GgkKm0Jg@mail.gmail.com>
 <CA+55aFyiJGk-A_cJH41Ec8Xj0Zz9M3EU-igJ9bgusj=nm28tFQ@mail.gmail.com>
From: Jens Axboe <axboe@fb.com>
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Date: Wed, 26 Oct 2016 17:03:45 -0600
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On 10/26/2016 04:58 PM, Linus Torvalds wrote:
> On Wed, Oct 26, 2016 at 3:51 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> Dave: it might be a good idea to split that "WARN_ON_ONCE()" in
>> blk_mq_merge_queue_io() into two
>
> I did that myself too, since Dave sees this during boot.
>
> But I'm not getting the warning ;(
>
> Dave gets it with ext4, and thats' what I have too, so I'm not sure
> what the required trigger would be.

Actually, I think I see what might trigger it. You are on nvme, iirc,
and that has a deep queue. Dave, are you testing on a sata drive or
something similar with a shallower queue depth? If we end up sleeping
for a request, I think we could trigger data->ctx being different.

Dave, can you hit the warnings with this? Totally untested...


diff --git a/block/blk-mq.c b/block/blk-mq.c
index ddc2eed64771..80a9c45a9235 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1217,9 +1217,7 @@ static struct request *blk_mq_map_request(struct 
request_queue *q,
  	blk_mq_set_alloc_data(&alloc_data, q, 0, ctx, hctx);
  	rq = __blk_mq_alloc_request(&alloc_data, op, op_flags);

-	hctx->queued++;
-	data->hctx = hctx;
-	data->ctx = ctx;
+	data->hctx->queued++;
  	return rq;
  }


-- 
Jens Axboe