linux-kernel - Re: [PATCH v3 4/5] btrfs: don't hold dev_replace rwsem over whole of btrfs_map

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Message-ID: <20240701141320.GI504479@perftesting>
Date: Mon, 1 Jul 2024 10:13:20 -0400
From: Josef Bacik <josef@...icpanda.com>
To: Johannes Thumshirn <jth@...nel.org>
Cc: Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Johannes Thumshirn <johannes.thumshirn@....com>
Subject: Re: [PATCH v3 4/5] btrfs: don't hold dev_replace rwsem over whole of
 btrfs_map_block

On Mon, Jul 01, 2024 at 12:25:18PM +0200, Johannes Thumshirn wrote:
> From: Johannes Thumshirn <johannes.thumshirn@....com>
> 
> Don't hold the dev_replace rwsem for the entirety of btrfs_map_block().
> 
> It is only needed to protect
> a) calls to find_live_mirror() and
> b) calling into handle_ops_on_dev_replace().
> 
> But there is no need to hold the rwsem for any kind of set_io_stripe()
> calls.
> 
> So relax taking the dev_replace rwsem to only protect both cases and check
> if the device replace status has changed in the meantime, for which we have
> to re-do the find_live_mirror() calls.
> 
> This fixes a deadlock on raid-stripe-tree where device replace performs a
> scrub operation, which in turn calls into btrfs_map_block() to find the
> physical location of the block.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>

Reviewed-by: Josef Bacik <josef@...icpanda.com>

Thanks,

Josef