From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Juri Lelli <juri.lelli@redhat.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Clark Williams <williams@redhat.com>
Subject: Re: [RT WARNING] DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current) with fsfreeze (4.19.25-rt16)
Date: Thu, 28 Mar 2019 11:17:26 +0100 [thread overview]
Message-ID: <20190328101726.u2y7v46mo66i5aoi@linutronix.de> (raw)
In-Reply-To: <20190326093421.GA29508@localhost.localdomain>
On 2019-03-26 10:34:21 [+0100], Juri Lelli wrote:
> Hi,
Hi,
…
> # for I in `seq 10`; do fsfreeze -f ./testmount; sleep 1; fsfreeze -u ./testmount; done
>
> ------------[ cut here ]------------
> DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current)
> WARNING: CPU: 10 PID: 1226 at kernel/locking/rtmutex-debug.c:145 debug_rt_mutex_unlock+0x9b/0xb0
> Modules linked in: xfs [...]
> CPU: 10 PID: 1226 Comm: fsfreeze Not tainted 4.19.25-rt16 #2
> Hardware name: LENOVO 30B6S2F900/1030, BIOS S01KT61A 09/28/2018
> RIP: 0010:debug_rt_mutex_unlock+0x9b/0xb0
…
> __rt_mutex_unlock+0x45/0x80
> percpu_up_write+0x4b/0x60
> thaw_super_locked+0xdb/0x110
…
> AFAIU, this is a legit warning, since
>
> fsfreeze -f ./testmount grabs rt_mutexes embedded into
> sb->s_writers.rw_sem[SB_FREEZE_LEVELS] (rt-rwsem) as part of executing
> sb_wait_write() (for each FREEZE_LEVEL) in freeze_super().
>
> We then return to userspace.
>
> fsfreeze -u ./testmount unlocks the rt_mutexes while doing
> sb_freeze_unlock() in thaw_super_locked(). This is a different process
> w.r.t. the one that did the freeze above.
>
> I noticed that a very similar problem was fixed (for !rt rwsem) by
> 5a817641f68a ("locking/percpu-rwsem: Annotate rwsem ownership transfer
> by setting RWSEM_OWNER_UNKNOWN"). However, RT has of course to deal with
> PI, so I wonder if there is an easy fix for this problem.
>
> Suggestions?
So we leave to userland with an acquired rtmutex. And lockdep doesn't
complain because lockdep_sb_freeze_release() /
lockdep_sb_freeze_acquire() informs that everything is okay.
I have no idea, PeterZ? The rwsem is not ownerless afaik.
> Thanks,
>
> - Juri
Sebastian
next prev parent reply other threads:[~2019-03-28 10:17 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-26 9:34 [RT WARNING] DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current) with fsfreeze (4.19.25-rt16) Juri Lelli
2019-03-28 10:17 ` Sebastian Andrzej Siewior [this message]
2019-04-19 8:56 ` Juri Lelli
2019-04-30 12:51 ` Sebastian Andrzej Siewior
2019-04-30 13:28 ` Peter Zijlstra
2019-04-30 13:45 ` Sebastian Andrzej Siewior
2019-04-30 14:01 ` Peter Zijlstra
2019-04-30 14:15 ` Oleg Nesterov
2019-04-30 14:29 ` Peter Zijlstra
2019-04-30 14:42 ` Oleg Nesterov
2019-04-30 14:44 ` Peter Zijlstra
2019-04-30 14:53 ` Oleg Nesterov
2019-05-01 17:09 ` Peter Zijlstra
2019-05-01 17:26 ` Waiman Long
2019-05-01 18:54 ` Peter Zijlstra
2019-05-01 19:22 ` Davidlohr Bueso
2019-05-01 19:25 ` Peter Zijlstra
2019-05-02 10:09 ` Oleg Nesterov
2019-05-02 11:42 ` Oleg Nesterov
2019-05-03 14:50 ` Peter Zijlstra
2019-05-03 15:25 ` Peter Zijlstra
2019-05-06 16:50 ` Oleg Nesterov
2019-06-19 9:50 ` Peter Zijlstra
2019-05-03 14:16 ` Peter Zijlstra
2019-05-03 15:37 ` Oleg Nesterov
2019-05-03 15:46 ` Peter Zijlstra
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