linux-kernel - Re: [PATCH AUTOSEL 4.19 11/12] gfs2: Refcounting fix in gfs2_thaw

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Date: Tue, 16 Jan 2024 21:46:54 +0100
From: Pavel Machek <pavel@...x.de>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Andreas Gruenbacher <agruenba@...hat.com>, gfs2@...ts.linux.dev
Subject: Re: [PATCH AUTOSEL 4.19 11/12] gfs2: Refcounting fix in
 gfs2_thaw_super

Hi!

> From: Andreas Gruenbacher <agruenba@...hat.com>
> 
> [ Upstream commit 4e58543e7da4859c4ba61d15493e3522b6ad71fd ]
> 
> It turns out that the .freeze_super and .thaw_super operations require
> the filesystem to manage the superblock refcount itself.  We are using
> the freeze_super() and thaw_super() helpers to mostly take care of that
> for us, but this means that the superblock may no longer be around by
> when thaw_super() returns, and gfs2_thaw_super() will then access freed
> memory.  Take an extra superblock reference in gfs2_thaw_super() to fix
> that.

Patch was broken during backport.

> +++ b/fs/gfs2/super.c
> @@ -1013,6 +1013,7 @@ static int gfs2_freeze(struct super_block *sb)
>  		goto out;
>  	}
>  
> +	atomic_inc(&sb->s_active);
>  	for (;;) {
>  		error = gfs2_lock_fs_check_clean(sdp, &sdp->sd_freeze_gh);
>  		if (!error)
> @@ -1034,6 +1035,7 @@ static int gfs2_freeze(struct super_block *sb)
>  	error = 0;
>  out:
>  	mutex_unlock(&sdp->sd_freeze_mutex);
> +	deactivate_super(sb);
>  	return error;
>  }

Notice the goto out? That now jumps around the atomic_inc, but we
still do decrease. This will break 4.19, please fix or drop.

BR,
								Pavel
-- 
DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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