linux-kernel - Re: [PATCH v2 1/6] super: remove pointless s

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Message-ID: <20250612-unbegreiflich-global-d7633c59da8e@brauner>
Date: Thu, 12 Jun 2025 14:20:54 +0200
From: Christian Brauner <brauner@...nel.org>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, jack@...e.cz, 
	linux-kernel@...r.kernel.org, James Bottomley <James.Bottomley@...senpartnership.com>, 
	mcgrof@...nel.org, hch@...radead.org, david@...morbit.com, rafael@...nel.org, 
	pavel@...nel.org, peterz@...radead.org, mingo@...hat.com, will@...nel.org, 
	boqun.feng@...il.com
Subject: Re: [PATCH v2 1/6] super: remove pointless s_root checks

On Wed, Jun 11, 2025 at 09:26:29AM -0700, Darrick J. Wong wrote:
> On Sat, Mar 29, 2025 at 09:42:14AM +0100, Christian Brauner wrote:
> > The locking guarantees that the superblock is alive and sb->s_root is
> > still set. Remove the pointless check.
> > 
> > Signed-off-by: Christian Brauner <brauner@...nel.org>
> > ---
> >  fs/super.c | 19 ++++++-------------
> >  1 file changed, 6 insertions(+), 13 deletions(-)
> > 
> > diff --git a/fs/super.c b/fs/super.c
> > index 97a17f9d9023..dc14f4bf73a6 100644
> > --- a/fs/super.c
> > +++ b/fs/super.c
> > @@ -930,8 +930,7 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
> >  
> >  		locked = super_lock_shared(sb);
> >  		if (locked) {
> > -			if (sb->s_root)
> > -				f(sb, arg);
> > +			f(sb, arg);
> >  			super_unlock_shared(sb);
> >  		}
> >  
> > @@ -967,11 +966,8 @@ void iterate_supers_type(struct file_system_type *type,
> >  		spin_unlock(&sb_lock);
> >  
> >  		locked = super_lock_shared(sb);
> > -		if (locked) {
> > -			if (sb->s_root)
> > -				f(sb, arg);
> > -			super_unlock_shared(sb);
> > -		}
> > +		if (locked)
> > +			f(sb, arg);
> 
> Hey Christian,
> 
> I might be trying to be the second(?) user of iterate_supers_type[1]. :)
> 
> This change removes the call to super_unlock_shared, which means that
> iterate_supers_type returns with the super_lock(s) still held.  I'm
> guessing that this is a bug and not an intentional change to require the
> callback to call super_unlock_shared, right?
> 
> --D
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=health-monitoring&id=3ae9b1d43dcdeaa38e93dc400d1871872ba0e27f

Yes, that's a bug. Can you send me a fix, please?