Re: [PATCH 05/17] btrfs: open block devices after superblock creation

[David Sterba <dsterba@suse.cz>]

On Fri, Aug 11, 2023 at 03:11:31PM +0200, David Sterba wrote:
> On Fri, Aug 11, 2023 at 02:44:50PM +0200, Christian Brauner wrote:
> > On Fri, Aug 11, 2023 at 12:08:16PM +0200, Christoph Hellwig wrote:
> > > Currently btrfs_mount_root opens the block devices before committing to
> > > allocating a super block. That creates problems for restricting the
> > > number of writers to a device, and also leads to a unusual and not very
> > > helpful holder (the fs_type).
> > > 
> > > Reorganize the code to first check whether the superblock for a
> > > particular fsid does already exist and open the block devices only if it
> > > doesn't, mirroring the recent changes to the VFS mount helpers.  To do
> > > this the increment of the in_use counter moves out of btrfs_open_devices
> > > and into the only caller in btrfs_mount_root so that it happens before
> > > dropping uuid_mutex around the call to sget.
> > > 
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > ---
> > 
> > Looks good to me,
> > Acked-by: Christian Brauner <brauner@kernel.org>
> > 
> > And ofc, would be great to get btrfs reviews.
> 
> I'll take a look but there are some performance regressions to deal with
> and pre-merge window freeze so it won't be soon.

I'd rather take the btrfs patches via my tree and get them tested for a
longer time.  This patch in particular changes locking, mount, device
management, that's beyond what I'd consider safe to get merged outside
of btrfs.