linux-kernel - Re: [PATCH 1/2] brw_mutex: big read-write mutex

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Message-ID: <CA+55aFwV-WOUx8MSr145f+HSrtmZ=nXHq0VLhtPyH=FNBFwmQg@mail.gmail.com>
Date:	Tue, 16 Oct 2012 12:56:58 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] brw_mutex: big read-write mutex

On Mon, Oct 15, 2012 at 12:10 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> This patch adds the new sleeping lock, brw_mutex. Unlike rw_semaphore
> it allows multiple writers too, just "read" and "write" are mutually
> exclusive.

So those semantics just don't sound sane. It's also not what any kind
of normal "rw" lock ever does.

So can you explain why these particular insane semantics are useful,
and what for?

                  Linus
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