From: TeJun Huh <tejun@aratech.co.kr>
To: Andrea Arcangeli <andrea@suse.de>
Cc: Stephan von Krawczynski <skraw@ithnet.com>,
manfred@colorfullife.com, linux-kernel@vger.kernel.org,
zwane@linuxpower.ca
Subject: Re: Possible race condition in i386 global_irq_lock handling.
Date: Sun, 24 Aug 2003 12:06:51 +0900 [thread overview]
Message-ID: <20030824030651.GA13292@atj.dyndns.org> (raw)
In-Reply-To: <20030822162546.GQ29612@dualathlon.random>
Hello Andrea,
On Fri, Aug 22, 2003 at 06:25:46PM +0200, Andrea Arcangeli wrote:
> thanks TeJun,
>
> just one comment
>
> On Fri, Aug 22, 2003 at 10:18:40AM +0900, TeJun Huh wrote:
> > 3. remove irqs_running() test from synchronize_irq()
>
> I'm not convinced this one is needed. An irq can still run on another
> cpu but the cli();sti() may execute while it's here:
>
> irq running synchronize_irq()
> -------------- -----------------
> do_IRQ
> handle_IRQ_event
> cli()
> sti()
>
> irq_enter -> way too late
>
> in short, doing irqs_running() doesn't seem to weaken the semantics of
> synchronize_irq() to me.
>
> I think it should be changed this way instead:
>
> void synchronize_irq(void)
> {
> smp_mb();
> if (irqs_running()) {
> /* Stupid approach */
> cli();
> sti();
> }
> }
>
> to be sure to read the local irq area after the previous code (the
> test_and_set_bit of the global_irq_lock of a cli() in your version would
> achieve the same implicit smp_mb too, so maybe your only point for doing
> cli()/sti() was to execute the smp_mb before the irqs_running?). the
> above version is more finegrined and it looks equivalent to yours.
>
> Andrea
Yes, you're right. Adding just smp_mb() should guarantee that no cpu
is executing interrupt handler which may not see memory contents
modified before synchronize_irq() after synchronize_irq() returns. I
think we need some decent comments there. :-)
As now I know that test_and_set_bit() implies memory barrier,
smb_mb__after_clear_bit() can be removed. I'll make and post a patch
which fixes this race and the bh race of the other thread.
Thanks.
--
tejun
next prev parent reply other threads:[~2003-08-24 3:05 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-08-21 17:01 Possible race condition in i386 global_irq_lock handling Manfred Spraul
2003-08-21 17:27 ` Andrea Arcangeli
2003-08-21 21:48 ` Stephan von Krawczynski
2003-08-21 22:44 ` Andrea Arcangeli
2003-08-22 1:18 ` TeJun Huh
2003-08-22 10:07 ` Stephan von Krawczynski
2003-08-22 16:25 ` Andrea Arcangeli
2003-08-24 3:06 ` TeJun Huh [this message]
2003-08-24 22:03 ` Andrea Arcangeli
-- strict thread matches above, loose matches on Subject: below --
2003-08-21 8:48 TeJun Huh
2003-08-21 10:07 ` Zwane Mwaikambo
2003-08-21 16:15 ` TeJun Huh
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=20030824030651.GA13292@atj.dyndns.org \
--to=tejun@aratech.co.kr \
--cc=andrea@suse.de \
--cc=linux-kernel@vger.kernel.org \
--cc=manfred@colorfullife.com \
--cc=skraw@ithnet.com \
--cc=zwane@linuxpower.ca \
/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;
as well as URLs for NNTP newsgroup(s).