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 [thread overview]
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!
prev parent reply other threads:[~2019-05-03 15:47 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
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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