linux-kernel - Re: [PATCH 4/4] mm, notifier: Catch sleeping/blocking for !blockable

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Message-ID: <20190822142410.GB8339@ziepe.ca>
Date:   Thu, 22 Aug 2019 11:24:10 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     LKML <linux-kernel@...r.kernel.org>, Linux MM <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 4/4] mm, notifier: Catch sleeping/blocking for !blockable

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

Jason