From: Sasha Levin <sashal@kernel.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Pavel Machek <pavel@denx.de>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
gfs2@lists.linux.dev
Subject: Re: [PATCH AUTOSEL 4.19 11/12] gfs2: Refcounting fix in gfs2_thaw_super
Date: Tue, 30 Jan 2024 16:16:09 -0500 [thread overview]
Message-ID: <ZblnGTNLbufz4gZx@sashalap> (raw)
In-Reply-To: <CAHc6FU70RD8fktBp=Srv6xeq3qXoLCdT8pi6y=1Y7bMHFK-mtQ@mail.gmail.com>
On Thu, Jan 18, 2024 at 12:50:37PM +0100, Andreas Gruenbacher wrote:
>On Tue, Jan 16, 2024 at 9:53 PM Pavel Machek <pavel@denx.de> wrote:
>> Hi!
>>
>> > From: Andreas Gruenbacher <agruenba@redhat.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.
>
>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.
I'll drop it, thanks!
--
Thanks,
Sasha
prev parent reply other threads:[~2024-01-30 21:16 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20240116002817.216837-1-sashal@kernel.org>
2024-01-16 0:28 ` [PATCH AUTOSEL 4.19 11/12] gfs2: Refcounting fix in gfs2_thaw_super Sasha Levin
2024-01-16 20:46 ` Pavel Machek
2024-01-18 11:50 ` Andreas Gruenbacher
2024-01-30 21:16 ` Sasha Levin [this message]
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