linux-kernel - Re: [RT WARNING] DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current) with fsfreeze (4.19.25-rt16)

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Message-ID: <20190430141500.GE23020@redhat.com>
Date:   Tue, 30 Apr 2019 16:15:01 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Clark Williams <williams@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>, jack@...e.com
Subject: Re: [RT WARNING] DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) !=
 current) with fsfreeze (4.19.25-rt16)

Sorry, I don't understand...

On 04/30, Peter Zijlstra wrote:
>
> Thaw then does the reverse, frobs lockdep

Yes, in particular it does

	lockdep_sb_freeze_acquire()
		percpu_rwsem_acquire()
			sem->rw_sem.owner = current;

	
> and then does: percpu_up_write().
>
> percpu_up_write() on up_write(). And note how __up_write() has:
>
> 	DEBUG_RWSEMS_WARN_ON(sem->owner != current, sem);

and everything looks correct, sem->owner == current by the time
thaw_super_locked() does percpu_up_write/up_write.

Oleg.