On Sat, 19 May 2007, David Brownell wrote: > > Absolutely right, I'm being an idiot here. I think I looked at root > > hub code in the rush to the FreedomHEC preparations. We do not have > > local_irq_save in the giveback routine. So, when Alan wrote "USB > > callbacks cannot be interrupted", he meant normal no-reentrancy > > guarantees, and not that the interrupts are disabled.
No, I really meant that interrupts are disabled. It's possible that I was wrong... > And by "normal no-reentrancy" you mean the normal guarantee that > each IRQ handler won't be re-entered while it's running. > > I observe that we don't register PCI IRQ handlers with IRQF_DISABLED, > so it's possible that some *other* IRQ happens while it's running; > but most of the non-PCI irq handlers are registered with that flag set. > > That seems potentially buglike to me; it's legit for any IRQ handler > to submit an URB. Which would then cause them to try grabbing the > spinlock held by the HCD's IRQ handler, if that "other" IRQ handler > happened to fire when the HCD's IRQ handler was running. > > So maybe we should always register with IRQF_DISABLED, unattractive > though that could be in terms of latencies ... or, somehow try to > define a rule whereby URBs can't be submitted in certain IRQ contexts. Or better still, always acquire the HCD's spinlock with spin_lock_irqsave(). That's what uhci-hcd does, even though ehci-hcd and ohci-hcd don't. Of course, if we don't use IRQF_DISABLED then we would have to verify that none of the callbacks rely on interrupts being disabled. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
