linux-kernel - Re: Mutex vs semaphores scheduler bug

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Message-ID: <24718.1255650266@redhat.com>
Date:	Fri, 16 Oct 2009 00:44:26 +0100
From:	David Howells <dhowells@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	dhowells@...hat.com,
	Török Edwin <edwin@...mav.net>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	aCaB <acab@...mav.net>, Nick Piggin <npiggin@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Mutex vs semaphores scheduler bug

Peter Zijlstra <peterz@...radead.org> wrote:

> The problem appears to be that rwsem doesn't allow lock-stealing

With good reason.  rwsems can be read or write locked for a long time - so if
readers can jump the queue on read-locked rwsems, then writer starvation is a
real possibility.  I carefully implemented it so that it is a strict FIFO to
avoid certain problems I was having.

David
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