linux-kernel - Re: [PATCH RESEND v2 1/1] percpu_rw_semaphore: reimplement to not block the readers unnecessarily

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Message-ID: <20121109181944.GA2078@redhat.com>
Date:	Fri, 9 Nov 2012 19:19:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	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 RESEND v2 1/1] percpu_rw_semaphore: reimplement to not
	block the readers unnecessarily

On 11/09, Oleg Nesterov wrote:
>
> 	static bool xxx(brw)
> 	{
> 		down_write(&brw->rw_sem);
> 		if (!atomic_read(&brw->slow_read_ctr))
>			return true;

I meant, try_to_down_write(). Otherwise this can obviously deadlock.

Oleg.

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