From: "Tony Battersby" <tonyb@cybernetics.com>
To: 'James Bottomley' <James.Bottomley@steeleye.com>
Cc: 'Alan Cox' <alan@lxorguk.ukuu.org.uk>,
'SCSI Mailing List' <linux-scsi@vger.kernel.org>,
marcelo@conectiva.com.br, dougg@torque.net
Subject: RE: [PATCH] 2.4.21 fix race condition in sg.c
Date: Fri, 27 Jun 2003 11:38:30 -0400 [thread overview]
Message-ID: <002b01c33cc2$2a353d40$e0019d89@cybernetics.com> (raw)
In-Reply-To: <1056726720.1825.27.camel@mulgrave>
> > Isn't smp_wmb() necessary to prevent the CPU from
> > re-ordering the stores?
>
> Ah, OK. The answer's yes and no. Your example is true for lockless
> access, but horribly racy (which is why, in practice, it's
> almost never
> done). The original code had locked access to done which prevents the
> race. If we've lost the locked access, I don't think the fix can be
> correct.
I looked at the locking before attempting the patch, but I didn't see
anything protecting the done flag or status return fields. It is true
that the done flag was set (without the patch) holding sg_dev_arr_lock,
but the code that looks at the done flag doesn't touch that lock.
If you think it needs a spinlock to be correct, then I will wait for
Doug's input, since he knows how it is supposed to work.
Anthony J. Battersby
Cybernetics
next prev parent reply other threads:[~2003-06-27 15:24 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
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 [this message]
-- 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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