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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>, boqun.feng@gmail.com
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	Ingo Molnar <mingo@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Mike Galbraith <efault@gmx.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [PATCH 3/4] locking/rwbase: Fix rwbase_write_lock() vs __rwbase_read_lock()
Date: Tue, 14 Sep 2021 09:45:12 +0200	[thread overview]
Message-ID: <87k0jjeh2v.ffs@tglx> (raw)
In-Reply-To: <20210909110203.893845303@infradead.org>

On Thu, Sep 09 2021 at 12:59, Peter Zijlstra wrote:

> Boqun noticed that the write-trylock sequence of load+set is broken in
> rwbase_write_lock()'s wait-loop since they're not both under the same
> wait_lock instance.

Confused.

lock(); A

for (; atomic_read(readers);) {
   ...
   unlock();
   ..
   lock(); B
}

atomic_set();
unlock(); A or B

The read/set is always in the same lock instance.

> Restructure the code to make this more obvious and correct.

I agree that it's easier to read, but I disagree that it makes the code
more correct.

Thanks,

        tglx

  reply	other threads:[~2021-09-14  7:46 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-09 10:59 [PATCH 0/4] locking/rwbase: Assorted fixes Peter Zijlstra
2021-09-09 10:59 ` [PATCH 1/4] sched/wakeup: Strengthen current_save_and_set_rtlock_wait_state() Peter Zijlstra
2021-09-09 13:45   ` Will Deacon
2021-09-09 14:27     ` Peter Zijlstra
2021-09-10 12:57       ` Will Deacon
2021-09-10 13:17         ` Peter Zijlstra
2021-09-10 14:01           ` Peter Zijlstra
2021-09-10 15:06             ` Will Deacon
2021-09-10 16:07             ` Waiman Long
2021-09-10 17:09               ` Peter Zijlstra
2021-09-12  3:57       ` Boqun Feng
2021-09-10 12:45   ` Sebastian Andrzej Siewior
2021-09-13 22:08   ` Thomas Gleixner
2021-09-13 22:52     ` Thomas Gleixner
2021-09-14  6:45       ` Peter Zijlstra
2021-09-09 10:59 ` [PATCH 2/4] locking/rwbase: Properly match set_and_save_state() to restore_state() Peter Zijlstra
2021-09-09 13:53   ` Will Deacon
2021-09-14  7:31   ` Thomas Gleixner
2021-09-16 11:59   ` [tip: locking/urgent] " tip-bot2 for Peter Zijlstra
2021-09-09 10:59 ` [PATCH 3/4] locking/rwbase: Fix rwbase_write_lock() vs __rwbase_read_lock() Peter Zijlstra
2021-09-14  7:45   ` Thomas Gleixner [this message]
2021-09-14 13:59     ` Peter Zijlstra
2021-09-14 15:00       ` Thomas Gleixner
2021-09-16 11:59       ` [tip: locking/urgent] locking/rwbase: Extract __rwbase_write_trylock() tip-bot2 for Peter Zijlstra
2021-09-09 10:59 ` [PATCH 4/4] locking/rwbase: Take care of ordering guarantee for fastpath reader Peter Zijlstra
2021-09-14  7:46   ` Thomas Gleixner
2021-09-16 11:59   ` [tip: locking/urgent] " tip-bot2 for Boqun Feng

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