[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <20071023032625.GA26559@gondor.apana.org.au>
Date: Tue, 23 Oct 2007 11:26:25 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
akpm@...ux-foundation.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linuxppc-dev@...abs.org, Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [IRQ]: Fix synchronize_irq races with IRQ handler
On Mon, Oct 22, 2007 at 07:10:05AM +1000, Benjamin Herrenschmidt wrote:
>
> Hrm... not on yet. Herbert, care to resend, looks like it fell down the
> wrong hole in Linus mailbox :-)
Thanks for the reminder Ben. Here it is again:
[IRQ]: Fix synchronize_irq races with IRQ handler
As it is some callers of synchronize_irq rely on memory barriers
to provide synchronisation against the IRQ handlers. For example,
the tg3 driver does
tp->irq_sync = 1;
smp_mb();
synchronize_irq();
and then in the IRQ handler:
if (!tp->irq_sync)
netif_rx_schedule(dev, &tp->napi);
Unfortunately memory barriers only work well when they come in
pairs. Because we don't actually have memory barriers on the
IRQ path, the memory barrier before the synchronize_irq() doesn't
actually protect us.
In particular, synchronize_irq() may return followed by the
result of netif_rx_schedule being made visible.
This patch (mostly written by Linus) fixes this by using spin
locks instead of memory barries on the synchronize_irq() path.
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Acked-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cheers,
--
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 80eab7a..1f31422 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -29,12 +29,28 @@
void synchronize_irq(unsigned int irq)
{
struct irq_desc *desc = irq_desc + irq;
+ unsigned int status;
if (irq >= NR_IRQS)
return;
- while (desc->status & IRQ_INPROGRESS)
- cpu_relax();
+ do {
+ unsigned long flags;
+
+ /*
+ * Wait until we're out of the critical section. This might
+ * give the wrong answer due to the lack of memory barriers.
+ */
+ while (desc->status & IRQ_INPROGRESS)
+ cpu_relax();
+
+ /* Ok, that indicated we're done: double-check carefully. */
+ spin_lock_irqsave(&desc->lock, flags);
+ status = desc->status;
+ spin_unlock_irqrestore(&desc->lock, flags);
+
+ /* Oops, that failed? */
+ } while (status & IRQ_INPROGRESS);
}
EXPORT_SYMBOL(synchronize_irq);
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists