linux-kernel - Re: [PATCH 4.19 196/245] nvme: fix possible deadlock when I/O is blocked

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Date:   Wed, 30 Sep 2020 18:22:54 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Anton Eidelman <anton@...htbitslabs.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Christoph Hellwig <hch@....de>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 196/245] nvme: fix possible deadlock when I/O is
 blocked

Hi!

> [ Upstream commit 3b4b19721ec652ad2c4fe51dfbe5124212b5f581 ]
> 
> Revert fab7772bfbcf ("nvme-multipath: revalidate nvme_ns_head gendisk
> in nvme_validate_ns")
> 
> When adding a new namespace to the head disk (via nvme_mpath_set_live)
> we will see partition scan which triggers I/O on the mpath device node.
> This process will usually be triggered from the scan_work which holds
> the scan_lock. If I/O blocks (if we got ana change currently have only
> available paths but none are accessible) this can deadlock on the head
> disk bd_mutex as both partition scan I/O takes it, and head disk revalidation
> takes it to check for resize (also triggered from scan_work on a different
> path). See trace [1].
> 
> The mpath disk revalidation was originally added to detect online disk
> size change, but this is no longer needed since commit cb224c3af4df
> ("nvme: Convert to use set_capacity_revalidate_and_notify") which already
> updates resize info without unnecessarily revalidating the disk (the
> mpath disk doesn't even implement .revalidate_disk fop).

Commit cb224c3af4df ("nvme: Convert to use
set_capacity_revalidate_and_notify") is not in 4.19-stable.

Does that mean we'll no longer detect disk size changes after this?

Best regards,
									Pavel

> index faa7feebb6095..84fcfcdb8ba5f 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -1599,7 +1599,6 @@ static void __nvme_revalidate_disk(struct gendisk *disk, struct nvme_id_ns *id)
>  	if (ns->head->disk) {
>  		nvme_update_disk_info(ns->head->disk, ns, id);
>  		blk_queue_stack_limits(ns->head->disk->queue, ns->queue);
> -		revalidate_disk(ns->head->disk);
>  	}
>  #endif
> 

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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