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From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
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)
Date: Fri, 3 May 2019 17:46:54 +0200
Message-ID: <20190503154654.GE2606@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190503153747.GC20802@redhat.com>

On Fri, May 03, 2019 at 05:37:48PM +0200, Oleg Nesterov wrote:
> (And if we change this code to use wait_event(xchg(readers_block) == 0) we
>  can remove rw_sem altogether).

That patch you just saw and didn't look at did just that.

> The main problem is that this is sub-optimal. We can have a lot of readers
> sleeping in __down_read() when percpu_down_write() succeeds, then after
> percpu_down_write_non_owner() does up_write() they all will be woken just
> to hang in readers_block(). Plus the new readers will need to pass the
> lock-check-unlock-schedule path.

Yes, that's gone. Still, write side locking on percpu-rwsem _should_ be
relatively rare and is certainly not a fast path.

> Peter, just in case... I see another patch from you but I need to run away
> till Monday.

n/p, enjoy the weekend!

      reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-26  9:34 Juri Lelli
2019-03-28 10:17 ` Sebastian Andrzej Siewior
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 [this message]

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