Re: [PATCH 1/3] mm: Check if mmu notifier callbacks are allowed to fail

From: Michal Hocko <mhocko@kernel.org>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: "Daniel Vetter" <daniel.vetter@ffwll.ch>,
	LKML <linux-kernel@vger.kernel.org>,
	"Linux MM" <linux-mm@kvack.org>,
	"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Christian König" <christian.koenig@amd.com>,
	"David Rientjes" <rientjes@google.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Daniel Vetter" <daniel.vetter@intel.com>
Subject: Re: [PATCH 1/3] mm: Check if mmu notifier callbacks are allowed to fail
Date: Fri, 23 Nov 2018 13:43:58 +0100	[thread overview]
Message-ID: <20181123124358.GJ8625@dhcp22.suse.cz> (raw)
In-Reply-To: <20181123123057.GK4266@phenom.ffwll.local>

On Fri 23-11-18 13:30:57, Daniel Vetter wrote:
> On Fri, Nov 23, 2018 at 12:15:57PM +0100, Michal Hocko wrote:
> > On Thu 22-11-18 17:51:04, Daniel Vetter wrote:
> > > Just a bit of paranoia, since if we start pushing this deep into
> > > callchains it's hard to spot all places where an mmu notifier
> > > implementation might fail when it's not allowed to.
> > 
> > What does WARN give you more than the existing pr_info? Is really
> > backtrace that interesting?
> 
> Automated tools have to ignore everything at info level (there's too much
> of that). I guess I could do something like
> 
> if (blockable)
> 	pr_warn(...)
> else
> 	pr_info(...)
> 
> WARN() is simply my goto tool for getting something at warning level
> dumped into dmesg. But I think the pr_warn with the callback function
> should be enough indeed.

I wouldn't mind s@pr_info@pr_warn@
 
> If you wonder where all the info level stuff happens that we have to
> ignore: suspend/resume is a primary culprit (fairly important for
> gfx/desktops), but there's a bunch of other places. Even if we ignore
> everything at info and below we still need filters because some drivers
> are a bit too trigger-happy (i915 definitely included I guess, so everyone
> contributes to this problem).

Thanks for the clarification.
-- 
Michal Hocko
SUSE Labs