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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Thu, 22 Aug 2019 16:27:18 +0200
Message-ID: <CAKMK7uF5CMSUrG2jTYJ9M7tDK_Saxmxk6yLs62tfc-Ozj3p2BQ@mail.gmail.com>
Subject: Re: [PATCH 4/4] mm, notifier: Catch sleeping/blocking for !blockable
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     LKML <linux-kernel@vger.kernel.org>, Linux MM <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>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Daniel Vetter <daniel.vetter@intel.com>
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On Thu, Aug 22, 2019 at 4:24 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Thu, Aug 22, 2019 at 10:42:39AM +0200, Daniel Vetter wrote:
>
> > > RDMA has a mutex:
> > >
> > > ib_umem_notifier_invalidate_range_end
> > >   rbt_ib_umem_for_each_in_range
> > >    invalidate_range_start_trampoline
> > >     ib_umem_notifier_end_account
> > >       mutex_lock(&umem_odp->umem_mutex);
> > >
> > > I'm working to delete this path though!
> > >
> > > nonblocking or not follows the start, the same flag gets placed into
> > > the mmu_notifier_range struct passed to end.
> >
> > Ok, makes sense.
> >
> > I guess that also means the might_sleep (I started on that) in
> > invalidate_range_end also needs to be conditional? Or not bother with
> > a might_sleep in invalidate_range_end since you're working on removing
> > the last sleep in there?
>
> I might suggest the same pattern as used for locked, the might_sleep
> unconditionally on the start, and a 2nd might sleep after the IF in
> __mmu_notifier_invalidate_range_end()
>
> Observing that by audit all the callers already have the same locking
> context for start/end

My question was more about enforcing that going forward, since you're
working to remove all the sleeps from invalidate_range_end. I don't
want to add debug annotations which are stricter than what the other
side actually expects. But since currently there is still sleeping
locks in invalidate_range_end I think I'll just stick them in both
places. You can then (re)move it when the cleanup lands.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch