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

[Mike Snitzer <snitzer@kernel.org>]

On Wed, Apr 17, 2024 at 09:32:55AM +0800, Ming Lei wrote:
> 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.

I normally would agree but I see no real reason to avoid leveraging
async fput() for the async DM device removal use-case ;)

Mike