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    SubjectRe: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic
    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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