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Subject: Re: [PATCH 2/2] block: hold queue lock while iterating in
 diskstats_show
To:     Daniel Wagner <dwagner@suse.de>, linux-block@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
References: <20220120105248.117025-1-dwagner@suse.de>
 <20220120105248.117025-3-dwagner@suse.de>
From:   Hannes Reinecke <hare@suse.de>
Message-ID: <bcd9ee08-d751-84f4-7334-b107ee3ca294@suse.de>
Date:   Thu, 20 Jan 2022 12:18:24 +0100
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Precedence: bulk

On 1/20/22 11:52 AM, Daniel Wagner wrote:
> The request queues can be freed while we operate on them. Make sure we
> hold a reference when using blk_mq_queue_tag_busy_iter.
> 
> RIP: blk_mq_queue_tag_busy_iter
> Call Trace:
>  ? blk_mq_hctx_mark_pending
>  ? diskstats_show
>  ? blk_mq_hctx_mark_pending
>  blk_mq_in_flight
>  diskstats_show
>  ? klist_next
>  seq_read
>  proc_reg_read
>  vfs_read
>  ksys_read
>  do_syscall_64
>  entry_SYSCALL_64_after_hwframe
> 
> Signed-off-by: Daniel Wagner <dwagner@suse.de>
> ---
>  block/genhd.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index c9d4386dd177..0e163055a4e6 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -1167,10 +1167,13 @@ static int diskstats_show(struct seq_file *seqf, void *v)
>  		if (bdev_is_partition(hd) && !bdev_nr_sectors(hd))
>  			continue;
>  		part_stat_read_all(hd, &stat);
> +		if (blk_queue_enter(gp->queue, BLK_MQ_REQ_NOWAIT))
> +			continue;
>  		if (queue_is_mq(gp->queue))
>  			inflight = blk_mq_in_flight(gp->queue, hd);
>  		else
>  			inflight = part_in_flight(hd);
> +		blk_queue_exit(gp->queue);
>  
>  		seq_printf(seqf, "%4d %7d %pg "
>  			   "%lu %lu %lu %u "
> 
While this looks good, it seems to have been cut against an earlier
branch; the code in question looks different in my copy.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
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