linux-ext4 - Re: [PATCH RFC 5/8] ext4: use super write guard in write_mmp

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Message-ID: <5puaizn2a4dpoinvkct2nz5zdvvv5vdrlrmwcz7j6vl7qrxicb@b4qi4yfk4a5u>
Date: Thu, 6 Nov 2025 10:24:40 +0100
From: Jan Kara <jack@...e.cz>
To: Daniel Vacek <neelx@...e.com>
Cc: Christian Brauner <brauner@...nel.org>, linux-fsdevel@...r.kernel.org, 
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, linux-btrfs@...r.kernel.org, 
	linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [PATCH RFC 5/8] ext4: use super write guard in write_mmp_block()

On Wed 05-11-25 19:33:35, Daniel Vacek wrote:
> On Tue, 4 Nov 2025 at 13:16, Christian Brauner <brauner@...nel.org> wrote:
> >
> > Signed-off-by: Christian Brauner <brauner@...nel.org>
> > ---
> >  fs/ext4/mmp.c | 8 ++------
> >  1 file changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
> > index ab1ff51302fb..6f57c181ff77 100644
> > --- a/fs/ext4/mmp.c
> > +++ b/fs/ext4/mmp.c
> > @@ -57,16 +57,12 @@ static int write_mmp_block_thawed(struct super_block *sb,
> >
> >  static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
> >  {
> > -       int err;
> > -
> >         /*
> >          * We protect against freezing so that we don't create dirty buffers
> >          * on frozen filesystem.
> >          */
> > -       sb_start_write(sb);
> > -       err = write_mmp_block_thawed(sb, bh);
> > -       sb_end_write(sb);
> > -       return err;
> > +       scoped_guard(super_write, sb)
> > +               return write_mmp_block_thawed(sb, bh);
> 
> Why the scoped_guard here? Should the simple guard(super_write)(sb) be
> just as fine here?

Not sure about Ted but I prefer scoped_guard() to plain guard() because the
scoping makes it more visually obvious where the unlocking happens. Of
course there has to be a balance as the indentation level can go through
the roof but that's not the case here...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR