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authorHerbert Xu <herbert@gondor.apana.org.au>2007-10-23 11:26:25 +0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-23 09:01:31 -0700
commita98ce5c6feead6bfedefabd46cb3d7f5be148d9a (patch)
tree7bbd027e40805966ad908e40f09ffd412a72a88b /kernel/irq
parent48d2268473a66fe3aa78fb13b09ee59d6ee95073 (diff)
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@gondor.apana.org.au> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/irq')
-rw-r--r--kernel/irq/manage.c20
1 files changed, 18 insertions, 2 deletions
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 80eab7a04205..1f314221d534 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);