On Wed, 20 Feb 2008, David Brownell wrote: > On Wednesday 20 February 2008, Alan Stern wrote: > > > ehci_hcd 0000:00:1d.7: IAA watchdog, lost IAA: status 8029 cmd 10021 > > > > lines in the log brings up some ideas that have been percolating in my > > mind for a while. They have to do with the possibility of a race > > between the watchdog routine and assertion of IAA. > > The curious bit IMO being STS_INT (0001), which should also have > triggered an IRQ. Suggesting to me that the race might be lower > level than that ... at the level of a conflict between the various > mechanisms to ack irqs.
Maybe it did trigger an IRQ. Inside the watchdog routine interrupts are disabled. > > In fact, if the timing comes out just wrong then it's possible (on SMP > > systems) for an IAA interrupt to arrive when the watchdog > > routine has already started running. Then end_unlink_async() might get > > called right at the start of a new IAA cycle, or when the reclaim list > > is empty. > > The driver's spinlock should prevent that particular problem from > appearing. I don't think so: CPU 0 CPU 1 ----- ----- Watchdog timer expires Timer routine acquires spinlock IAA IRQ arrives ehci_irq tries to acquire spinlock... Timer routine either sets ehci->reclaim to NULL or else starts a new IAA cycle Timer routine releases spinlock and returns ehci_irq acquires spinlock and sees IAA is set Call end_unlink_async()! > ========= CUT HERE > Modify EHCI irq handling on the theory that at least some of the > "lost" IRQs are caused by goofage between multiple lowlevel IRQ > acking mechanisms: try rescanning before we exit the handler, in > case the EHCI-internal ack (by clearing the irq status) doesn't > always suffice for IRQs triggered nearly back-to-back. This might help, but it won't fix the race outlined above. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/