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

[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.
Which is really the point of the patch you are trying to revert.
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