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Date:   Tue, 20 Apr 2021 13:03:35 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     rafael@kernel.org, gregkh@linuxfoundation.org,
        viro@zeniv.linux.org.uk, jack@suse.cz, bvanassche@acm.org,
        jeyu@kernel.org, ebiederm@xmission.com, mchehab@kernel.org,
        keescook@chromium.org, linux-fsdevel@vger.kernel.org,
        kernel@tuxforce.de, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, Dave Chinner <david@fromorbit.com>
Subject: Re: [RFC v2 1/6] fs: provide unlocked helper for freeze_super()
Message-ID: <20210420120335.GA3604224@infradead.org>
References: <20210417001026.23858-1-mcgrof@kernel.org>
 <20210417001026.23858-2-mcgrof@kernel.org>
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On Sat, Apr 17, 2021 at 12:10:21AM +0000, Luis Chamberlain wrote:
> freeze_super() holds a write lock, however we wish to also enable
> callers which already hold the write lock. To do this provide a helper
> and make freeze_super() use it. This way, all that freeze_super() does
> now is lock handling and active count management.

Can we take a step back and think about this a bit more?

freeze_super() has three callers:

 1) freeze_bdev
 2) ioctl_fsfreeze
 3) freeze_store (in gfs2)

The first gets its reference from get_active_super, and is the only
caller of get_active_super.  So IMHO we should just not drop the lock
in get_active_super and directly call the unlocked version.

The other two really should just call grab_super to get an active
reference and s_umount.

In other words: I don't think we need both variants, just move the
locking and s_active acquisition out of free_super.  Same for the
thaw side.