From: James Bottomley <James.Bottomley@steeleye.com>
To: tonyb@cybernetics.com
Cc: marcelo@conectiva.com.br, Alan Cox <alan@lxorguk.ukuu.org.uk>,
SCSI Mailing List <linux-scsi@vger.kernel.org>,
dougg@torque.net
Subject: Re: [PATCH] 2.4.21 fix race condition in sg.c
Date: 27 Jun 2003 09:10:51 -0500 [thread overview]
Message-ID: <1056723054.1825.16.camel@mulgrave> (raw)
In-Reply-To: <002901c33cb3$4b262730$e0019d89@cybernetics.com>
On Fri, 2003-06-27 at 08:52, Tony Battersby wrote:
> Note: I have added smp_wmb() since the last time I sent this patch. I think
> it is necessary for 100% correctness.
Actually, I don't believe it is. memory barriers are only needed if the
code cares about the ordering of the write. Either for externally
visible ordering (like MMIO to a device, or other CPU visibility in SMP)
or for internal consistency to prevent gcc reordering the writes to give
states that could be temporarily bogus.
I don't believe any of the above applies to the sg request pointer done
flag.
Memory barriers can be expensive on some architectures, so it's best to
use them only where necessary.
James
next prev parent reply other threads:[~2003-06-27 13:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-06-27 13:52 [PATCH] 2.4.21 fix race condition in sg.c Tony Battersby
2003-06-27 14:10 ` James Bottomley [this message]
2003-06-27 14:31 ` Alan Cox
2003-06-27 14:47 ` James Bottomley
2003-06-27 14:57 ` Tony Battersby
2003-06-27 15:00 ` Jeff Garzik
2003-06-27 15:11 ` James Bottomley
2003-06-27 15:38 ` Tony Battersby
-- strict thread matches above, loose matches on Subject: below --
2003-06-26 15:18 Tony Battersby
2003-06-26 22:15 ` Douglas Gilbert
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