From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org,
orgis@agnld.uni-potsdam.de, arekm@maven.pl, ed.lin@promise.com,
Andrew Morton <akpm@linux-foundation.org>,
James.Bottomley@SteelEye.com
Subject: Re: [PATCH] Fix race with shared tag queue maps
Date: Thu, 13 Sep 2007 08:16:52 -0700 (PDT) [thread overview]
Message-ID: <alpine.LFD.0.999.0709130813220.16478@woody.linux-foundation.org> (raw)
In-Reply-To: <20070913122652.GK25592@kernel.dk>
On Thu, 13 Sep 2007, Jens Axboe wrote:
> +
> + /*
> + * Ensure ordering with tag section
> + */
> + smp_mb__before_clear_bit();
> +
> + if (unlikely(!test_and_clear_bit(tag, bqt->tag_map))) {
You don't need the "smp_mb__before_clear_bit()" there.
The regular "clear_bit()" needs it, but the "test_and_xxx()" versions are
architecturally defined to be memory barriers, exactly because they are
regularly used for locking.
This is even documented - see Documentation/atomic_ops.txt.
Linus
next prev parent reply other threads:[~2007-09-13 15:19 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-13 12:26 Jens Axboe
2007-09-13 15:16 ` Linus Torvalds [this message]
2007-09-13 15:22 ` Jens Axboe
2007-09-13 15:42 ` Linus Torvalds
2007-09-14 7:47 ` Jens Axboe
2007-09-14 6:19 ` Arkadiusz Miskiewicz
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