linux-kernel - Re: [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable

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Date:   Wed, 14 Aug 2019 21:00:29 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Christian König <christian.koenig@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable

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?

Jason