Messages in this thread | | | Subject | Re: [PATCH] synchronize_irq needs a barrier | From | Benjamin Herrenschmidt <> | Date | Thu, 18 Oct 2007 12:57:15 +1000 |
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> > In general, I tend to think that for this function to make any sense > (that is, to synchronize anything at all), it needs a barrier or you are > just making a decision based on a totally random value of desc->status > since it can have been re-ordered, speculatively loaded, pre-fetched, > whatever'ed... :-).
Take a real life example:
drivers/message/fusion/mptbase.c
/* Disable interrupts! */ CHIPREG_WRITE32(&ioc->chip->IntMask, 0xFFFFFFFF);
ioc->active = 0; synchronize_irq(pdev->irq);
And we aren't in a spinlock here.
That's just a random example grepped.... I think I see a few more. Then, some drivers like tg3 actually do an smp_mb() before calling synchronize_irq(). But then, some don't.
I think trying to have all drivers be correct here is asking for trouble, we'd rather have synchronize_irq() be uber-safe. It's not like it was used in hot path anyway.
Ben.
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