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SubjectRe: [PATCH 2/2] block: hold queue lock while iterating in diskstats_show
On Thu, Jan 20, 2022 at 11:52:48AM +0100, Daniel Wagner wrote:
> The request queues can be freed while we operate on them. Make sure we

It shouldn't be freed here.

> hold a reference when using blk_mq_queue_tag_busy_iter.
>
> RIP: blk_mq_queue_tag_busy_iter

Any chance to pose the whole stack trace?

> 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;

The disk device's refcnt is supposed to be grabbed by class device
iterator code, so queue shouldn't be released in diskstats_show().

Not mention blk_queue_enter() won't prevent disk from being released...

thanks,
Ming

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