linux-kernel - Re: [PATCH v2] kref: warn on uninitialized kref

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Message-ID: <20140519081946.GV30445@twins.programming.kicks-ass.net>
Date:	Mon, 19 May 2014 10:19:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Bart Van Assche <bvanassche@....org>,
	Mateusz Guzik <mguzik@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	linux-scsi@...r.kernel.org, target-devel@...r.kernel.org
Subject: Re: [PATCH v2] kref: warn on uninitialized kref

On Sat, May 17, 2014 at 05:14:13PM -0400, Mikulas Patocka wrote:
> BTW. if we talk about performance - what about replacing:
> 
> 	if (atomic_dec_and_test(&variable)) {
> 		... release(object);
> 	}
> 
> with this:
> 
> 	if (atomic_read(&variable) == 1 || atomic_dec_and_test(&variable)) {
> 		barrier();
> 		... release(object);
> 	}

That would completely wreck kref_get_unless_zero().

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