linux-kernel - Re: [PATCH] block: fix deadlock between bd_link_disk

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Date: Tue, 20 Feb 2024 09:09:17 +0100
From: Christoph Hellwig <hch@....de>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: linan666@...weicloud.com, axboe@...nel.dk,
	Christoph Hellwig <hch@....de>, "yukuai (C)" <yukuai3@...wei.com>,
	linux-raid@...r.kernel.org, song@...nel.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	yi.zhang@...wei.com, houtao1@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH] block: fix deadlock between bd_link_disk_holder and
 partition scan

On Mon, Feb 19, 2024 at 04:53:36PM +0800, Yu Kuai wrote:
> Can you take a look at this patch? I think for raid(perhaps and dm and
> other drivers), it's reasonable to suspend IO while hot adding new
> underlying disks. And I think add new slaves to holder is not related to
> open the holder disk, because caller should already open the holder disk
> to hot add slaves, hence 'open_mutex' for holder is not necessary here.
>
> Actually bd_link_disk_holder() is protected by 'reconfig_mutex' for
> raid, and 'table_devices_lock' for dm(I'm not sure yet if other drivers
> have similiar lock).
>
> For raid, we do can fix this problem in raid by delay
> bd_link_disk_holder() while the array is not suspended, however, we'll
> consider this fix later if you think this patch is not acceptable.

Yes, not taking open_lock here seems reasonable, open_lock or it's
previous name has always been a bit of a catchall without very well
defined semantics.  I'd give the symbol a blk_ prefix, though.