linux-kernel - Re: bio linked list corruption.

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Message-ID: <2bdc068d-afd5-7a78-f334-26970c91aaca@fb.com>
Date:   Wed, 26 Oct 2016 17:03:45 -0600
From:   Jens Axboe <axboe@...com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Jones <davej@...emonkey.org.uk>, Chris Mason <clm@...com>,
        Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>, Josef Bacik <jbacik@...com>,
        David Sterba <dsterba@...e.com>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Dave Chinner <david@...morbit.com>
Subject: Re: bio linked list corruption.

On 10/26/2016 04:58 PM, Linus Torvalds wrote:
> On Wed, Oct 26, 2016 at 3:51 PM, Linus Torvalds
> <torvalds@...ux-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