From: James Bottomley <James.Bottomley@steeleye.com>
To: tonyb@cybernetics.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: 27 Jun 2003 10:11:59 -0500 [thread overview]
Message-ID: <1056726720.1825.27.camel@mulgrave> (raw)
In-Reply-To: <002a01c33cbc$5e45d960$e0019d89@cybernetics.com>
On Fri, 2003-06-27 at 09:57, Tony Battersby wrote:
> > I don't believe any of the above applies to the sg request
> > pointer done flag.
>
> I see a situation analogous to this:
>
> CPU #0:
> foo = result;
> smp_wmb();
> done = 1;
>
> CPU #1:
> if (done)
> return foo;
> 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.
James
next prev parent reply other threads:[~2003-06-27 14:57 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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1056726720.1825.27.camel@mulgrave \
--to=james.bottomley@steeleye.com \
--cc=alan@lxorguk.ukuu.org.uk \
--cc=dougg@torque.net \
--cc=linux-scsi@vger.kernel.org \
--cc=marcelo@conectiva.com.br \
--cc=tonyb@cybernetics.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox