lkml.org 
[lkml]   [2003]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Possible race condition in i386 global_irq_lock handling.
 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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:48    [W:0.065 / U:1.808 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site