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Date:   Thu, 2 May 2019 13:42:59 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        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>,
        Juri Lelli <juri.lelli@redhat.com>, jack@suse.com,
        Waiman Long <longman@redhat.com>,
        Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [RT WARNING] DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) !=
 current) with fsfreeze (4.19.25-rt16)
Message-ID: <20190502114258.GB7323@redhat.com>
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On 05/02, Oleg Nesterov wrote:
>
> But this all is cosmetic, it seems that we can remove ->rw_sem altogether
> but I am not sure...

I mean, afaics percpu_down_read() can just do

	wait_event(readers_block == 0);

in the slow path, while percpu_down_write()

	wait_even_exclusive(xchg(readers_block, 1) == 0);

we do not really need ->rw_sem if we rely on wait_queue_head.


But in fact, either way it seems that we going to implement another simple
"non owner" read/write lock, so perhaps we should do this explicitly?

Oleg.