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Date: Wed, 26 Oct 2016 19:38:08 -0400
From: Chris Mason <clm@fb.com>
To: Jens Axboe <axboe@fb.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Jones <davej@codemonkey.org.uk>,
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        Dave Chinner <david@fromorbit.com>
Subject: Re: bio linked list corruption.
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On Wed, Oct 26, 2016 at 05:20:01PM -0600, Jens Axboe wrote:
>On 10/26/2016 05:08 PM, Linus Torvalds wrote:
>>On Wed, Oct 26, 2016 at 4:03 PM, Jens Axboe <axboe@fb.com> wrote:
>>>
>>>Actually, I think I see what might trigger it. You are on nvme, iirc,
>>>and that has a deep queue.
>>
>>Yes. I have long since moved on from slow disks, so all my systems are
>>not just flash, but m.2 nvme ssd's.
>>
>>So at least that could explain why Dave sees it at bootup but I don't.
>
>Yep, you'd never sleep during normal boot. The original patch had a
>problem, though... This one should be better. Too many 'data's, we'll
>still need to assign ctx/hctx, we should just use the current ones, not
>the original ones.
>
>diff --git a/block/blk-mq.c b/block/blk-mq.c
>index ddc2eed64771..e56fec187ba6 100644
>--- a/block/blk-mq.c
>+++ b/block/blk-mq.c
>@@ -1217,9 +1224,9 @@ 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 = alloc_data.hctx;
>+	data->ctx = alloc_data.ctx;
>+	data->hctx->queued++;
> 	return rq;
> }

This made it through an entire dbench 2048 run on btrfs.  My script has 
it running in a loop, but this is farther than I've gotten before.  
Looking great so far.

-chris