From: Oleg Nesterov <oleg@redhat.com>
To: Christian Brauner <brauner@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>,
Hillf Danton <hdanton@sina.com>,
paulmck@kernel.org, rcu@vger.kernel.org
Subject: Re: rcu_sync_dtor() warning question
Date: Mon, 29 Jul 2024 11:02:52 +0200 [thread overview]
Message-ID: <20240729090226.GB8691@redhat.com> (raw)
In-Reply-To: <20240729-imponieren-webstuhl-8ed39923df25@brauner>
On 07/29, Christian Brauner wrote:
>
> On Sun, Jul 28, 2024 at 03:41:01PM GMT, Oleg Nesterov wrote:
> >
> > So in this case thaw_super_locked() just clears sb->s_writers.frozen and
> > goes to the "out_deactivate" label bypassing sb_freeze_unlock().
...
> So that would mean freeze_super() would've indeed acquired
> percpu_down_write(SB_FREEZE_WRITE+SB_FREEZE_PAGEFAULT+SB_FREEZE_FS) but
> thaw_super() would skip calling
> sb_freeze_unlock(SB_FREEZE_FS+SB_FREEZE_PAGEFAULT+SB_FREEZE_WRITE) and
> destroying the superblock during umount with an imbalance that gets
> noticed in rcu_sync_dtor().
>
> So afaict this would mean that we never called rcu_sync_exit() and thus
> never set GP_EXIT and notice that imbalance during rcu_sync_dtor().
Yes, yes, this is what I meant.
Oleg.
next prev parent reply other threads:[~2024-07-29 9:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20240726-ansonsten-piste-c4f04d4909fc@brauner>
2024-07-26 18:02 ` rcu_sync_dtor() warning question Paul E. McKenney
2024-07-26 18:39 ` Mateusz Guzik
2024-07-26 18:43 ` Mateusz Guzik
2024-07-26 20:21 ` Paul E. McKenney
2024-07-28 13:41 ` Oleg Nesterov
2024-07-29 8:25 ` Christian Brauner
2024-07-29 9:02 ` Oleg Nesterov [this message]
2024-07-29 8:28 ` Christian Brauner
2024-07-29 8:26 ` Christian Brauner
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