On Wed, Nov 26, 2014 at 05:51:08PM +0100, Christian Borntraeger wrote: > > But this one was > giving users in field false positives. > > So lets try to fix those, ok? If we cant, then tough luck. Sure. I think the simplest way might be to make spinlock disable premption when CONFIG_DEBUG_ATOMIC_SLEEP is enabled. As a result, userspace access will fail and caller will get a nice error. > But coming up with wrong statements is not helpful. True. Sorry that I did that. > > > > The point is that *_user is safe with preempt off. > > It returns an error gracefully. > > It does not sleep. > > It does not trigger the scheduler in that context. > > There are special cases where your statement is true. But its not in general. > copy_to_user might fault and that fault might sleep and reschedule. Yes. But not if called inatomic. > For example handle_mm_fault might go down to pud_alloc, pmd_alloc etc and all these functions could do an GFP_KERNEL allocation. Which might sleep. Which will schedule. > > > > > > > > David's patch makes it say it does, so it's wrong. > > > > > > Absolutely. I think you can already debug your case easily, by enabling CONFIG_PREEMPT. This seems counter-intuitive, and distro debug kernels don't seem to do this. -- 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
