lkml.org 
[lkml]   [2014]   [Nov]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
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


\
 
 \ /
  Last update: 2014-11-26 17:01    [W:0.243 / U:0.024 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site