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Date:   Thu, 15 Aug 2019 09:02:49 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        DRI Development <dri-devel@lists.freedesktop.org>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        David Rientjes <rientjes@google.com>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable
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        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
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        Michal Hocko <mhocko@suse.com>,
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        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
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        Daniel Vetter <daniel.vetter@intel.com>
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 <20190815000029.GC11200@ziepe.ca>
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On Wed, Aug 14, 2019 at 09:00:29PM -0300, Jason Gunthorpe wrote:
> On Wed, Aug 14, 2019 at 10:20:25PM +0200, Daniel Vetter wrote:
> > We need to make sure implementations don't cheat and don't have a
> > possible schedule/blocking point deeply burried where review can't
> > catch it.
> > 
> > I'm not sure whether this is the best way to make sure all the
> > might_sleep() callsites trigger, and it's a bit ugly in the code flow.
> > But it gets the job done.
> > 
> > Inspired by an i915 patch series which did exactly that, because the
> > rules haven't been entirely clear to us.
> 
> I thought lockdep already was able to detect:
> 
>  spin_lock()
>  might_sleep();
>  spin_unlock()
> 
> Am I mistaken? If yes, couldn't this patch just inject a dummy lockdep
> spinlock?

Hm ... assuming I didn't get lost in the maze I think might_sleep (well
___might_sleep) doesn't do any lockdep checking at all. And we want
might_sleep, since that catches a lot more than lockdep.

Maybe you mixed it up with the hard/softirq context stuff that lockdep
tracks and complains about if you get it wrong?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch