On Tue, Jan 16, 2024 at 9:53 PM Pavel Machek <pavel@xxxxxxx> wrote:
> Hi!
>
> > From: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
> >
> > [ 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.
Thanks, Pavel.
Sasha, you don't want that fix without "gfs2: Rework freeze / thaw
logic" and the follow-up fixes, and backporting that probably isn't
going to be worth it.
Thanks,
Andreas
