On Wednesday, 26 of March 2008, Alan Stern wrote: > On Tue, 25 Mar 2008, Rafael J. Wysocki wrote: > > > > I just thought of another problem. At the point where > > > local_irq_disable() is called, in between device_suspend() and > > > device_power_down(), it is possible in a preemptible kernel that > > > another task is holding dpm_list_mtx and is in the middle of updating > > > the list pointers. This would mess up the traversal in > > > device_power_down(). > > > > > > I'm not sure about the best way to prevent this. Is it legal to call > > > unlock_mutex() while interrupts or preemption are disabled? > > > > Well, I think it is, but I'm not sure how that can help. > > > > To prevent the race from happening, we can lock dpm_list_mtx before switching > > interrupts off in kernel/power/main.c:suspend_enter() and analogously in > > kernel/power/disk.c . > > That's right. And once interrupts are turned off you should unlock > dpm_list_mtx again, in case a noirq method wants to unregister a > device. Why would a noirq method want to do that? IMO, it's not a big deal if noirq methods are not allowed to unregister devices. > Hence my question: Is it legal to call unlock_mutex() while interrupts are > disabled? Well, I suspect that will confuse lockdep quite a bit. Otherwise, I don't see a problem with it (it's just changing the value of a shared variable after all). Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
