linux-kernel - Re: [PATCH] kernfs: Move faulting copy_user operations outside of the mutex

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Message-ID: <1459491088.4199.2.camel@linux.intel.com>
Date:	Fri, 01 Apr 2016 09:11:28 +0300
From:	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Tejun Heo <tj@...nel.org>, Chris Wilson <chris@...is-wilson.co.uk>,
	Daniel Vetter <daniel.vetter@...el.com>,
	intel-gfx@...ts.freedesktop.org,
	Ville Syrjälä 
	<ville.syrjala@...ux.intel.com>, NeilBrown <neilb@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernfs: Move faulting copy_user operations outside of
 the mutex

On to, 2016-03-31 at 13:15 -0700, Greg Kroah-Hartman wrote:
> On Thu, Mar 31, 2016 at 08:30:05PM +0300, Joonas Lahtinen wrote:
> > 
> > On to, 2016-03-31 at 12:49 -0400, Tejun Heo wrote:
> > > 
> > > On Thu, Mar 31, 2016 at 11:45:06AM +0100, Chris Wilson wrote:
> > > > 
> > > > 
> > > > A fault in a user provided buffer may lead anywhere, and lockdep warns
> > > > that we have a potential deadlock between the mm->mmap_sem and the
> > > > kernfs file mutex:
> > > ...
> > > > 
> > > > 
> > > > Reported-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94350
> > > > Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
> > > > Reviewed-by: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> > > > Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > > > Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> > > > Cc: Tejun Heo <tj@...nel.org>
> > > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > > Cc: NeilBrown <neilb@...e.de>
> > > > Cc: linux-kernel@...r.kernel.org
> > > Acked-by: Tejun Heo <tj@...nel.org>
> > > 
> > Thanks.
> > 
> > I have applied this locally to our repo to be included into our CI
> > builds.
> > 
> > We will drop the local patch once this waterfalls from upstream to our
> > drm-intel-nightly repo.
> So is this something that needs to get into 4.6-final because it
> resolves a reported issue?  Or can it wait for 4.7-rc1?
> 

It is only a getting rid of a lockdep splat describing a scenario very
unlikely to ever happen, so it can wait for 4.7-rc1.

Regards, Joonas

> thanks,
> 
> greg k-h
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation