On Wed, Nov 26, 2014 at 04:30:32PM +0100, Christian Borntraeger wrote: > Am 26.11.2014 um 16:17 schrieb Michael S. Tsirkin: > > On Wed, Nov 26, 2014 at 11:05:04AM +0100, David Hildenbrand wrote: > >>> What's the path you are trying to debug? > >> > >> Well, we had a problem where we held a spin_lock and called > >> copy_(from|to)_user(). We experienced very random deadlocks that took some guy > >> almost a week to debug. The simple might_sleep() check would have showed this > >> error immediately. > > > > > This must have been a very old kernel. > > A modern kernel will return an error from copy_to_user. > > I disagree. copy_to_user will not return while holding a spinlock, because it does not know! How should it? > See: spin_lock will call preempt_disable, but thats a no-op for a non-preempt kernel. So the mere fact that we hold a spin_lock is not known by any user access function. (or others). No? > > Christian > > Well might_sleep() merely checks preempt count and irqs_disabled too. If you want debugging things to trigger, you need to enable a bunch of config options. That's not new. -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
