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

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Message-ID: <20181123124358.GJ8625@dhcp22.suse.cz>
Date:   Fri, 23 Nov 2018 13:43:58 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian König <christian.koenig@....com>,
        David Rientjes <rientjes@...gle.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 1/3] mm: Check if mmu notifier callbacks are allowed to
 fail

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@...info@...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