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

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Message-ID: <20190821161635.GC8653@ziepe.ca>
Date:   Wed, 21 Aug 2019 13:16:35 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     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 Wed, Aug 21, 2019 at 05:41:51PM +0200, Daniel Vetter wrote:

> > Hm, I thought the page table locks we're holding there already prevent any
> > sleeping, so would be redundant? But reading through code I think that's
> > not guaranteed, so yeah makes sense to add it for invalidate_range_end
> > too. I'll respin once I have the ack/nack from scheduler people.
> 
> So I started to look into this, and I'm a bit confused. There's no
> _nonblock version of this, so does this means blocking is never allowed,
> or always allowed?

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.

> From a quick look through implementations I've only seen spinlocks, and
> one up_read. So I guess I should wrape this callback in some unconditional
> non_block_start/end, but I'm not sure.

For now, we should keep it the same as start, conditionally blocking.

Hopefully before LPC I can send a RFC series that eliminates most
invalidate_range_end users in favor of common locking..

Jason