linux-kernel - Re: [PATCH v3 3/4] locking/rwsem: Improve reader wakeup code

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Message-ID: <573B5530.2060301@hurleysoftware.com>
Date:	Tue, 17 May 2016 10:30:24 -0700
From:	Peter Hurley <peter@...leysoftware.com>
To:	Waiman Long <Waiman.Long@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Davidlohr Bueso <dave@...olabs.net>,
	Jason Low <jason.low2@...com>,
	Dave Chinner <david@...morbit.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH v3 3/4] locking/rwsem: Improve reader wakeup code

On 05/12/2016 03:56 PM, Waiman Long wrote:
> In __rwsem_do_wake(), the reader wakeup code will assume a writer
> has stolen the lock if the active reader/writer count is not 0.
> However, this is not as reliable an indicator as the original
> "< RWSEM_WAITING_BIAS" check. If another reader is present, the code
> will still break out and exit even if the writer is gone. This patch
> changes it to check the same "< RWSEM_WAITING_BIAS" condition to
> reduce the chance of false positive.

Nice.

Reviewed-by: Peter Hurley <peter@...leysoftware.com>