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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 26 Nov 2014 17:17:29 +0200

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.