Commit a98ce5c6 authored Oct 23, 2007 by Herbert Xu Committed by Linus Torvalds Oct 23, 2007

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>

parent 48d22684

kernel/irq/manage.c

+18 −2

Original line number	Diff line number	Diff line
		@@ -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;

		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);

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