Re: [PATCH v3 4/5] btrfs: don't hold dev_replace rwsem over whole of btrfs_map_block

[Josef Bacik <josef@toxicpanda.com>]

On Mon, Jul 01, 2024 at 12:25:18PM +0200, Johannes Thumshirn wrote:
> From: Johannes Thumshirn <johannes.thumshirn@wdc.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@wdc.com>

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

Thanks,

Josef