From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Tue, 23 Oct 2007 03:26:25 +0000 (+0800)
Subject: Fix synchronize_irq races with IRQ handler
X-Git-Tag: v2.6.24-rc1~29
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a98ce5c6feead6bfedefabd46cb3d7f5be148d9a;p=pandora-kernel.git

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>
---

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