Re: [PATCH v2] dm: restore synchronous close of device mapper block device

[Ming Lei <ming.lei@redhat.com>]

On Tue, Apr 16, 2024 at 11:28:42AM -0400, Mike Snitzer wrote:
> From: Ming Lei <ming.lei@redhat.com>
> 
> 'dmsetup remove' and 'dmsetup remove_all' require synchronous bdev
> release. Otherwise dm_lock_for_deletion() may return -EBUSY if the open
> count is > 0, because the open count is dropped in dm_blk_close()
> which occurs after fput() completes.
> 
> So if dm_blk_close() is delayed because of asynchronous fput(), this
> device mapper device is skipped during remove, which is a regression.
> 
> Fix the issue by using __fput_sync().
> 
> Also: DM device removal has long supported being made asynchronous by
> setting the DMF_DEFERRED_REMOVE flag on the DM device. So leverage
> using async fput() in close_table_device() if DMF_DEFERRED_REMOVE flag
> is set.

IMO, this way isn't necessary, because the patch is one bug fix, and we are
supposed to recover into exact previous behavior before commit a28d893eb327
("md: port block device access to file") for minimizing regression risk.

But the extra change seems work.


thanks, 
Ming