Messages in this thread | | | Date | Wed, 26 Nov 2014 17:23:34 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic |
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On Wed, Nov 26, 2014 at 05:17:29PM +0200, Michael S. Tsirkin wrote: > 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. > Which is really the point of the patch you are trying to revert.
That's assuming you disabled preemption. If you didn't, and take a spinlock, you have deadlocks even without userspace access.
-- MST
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