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Date:   Wed, 21 Aug 2019 13:16:35 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     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>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>,
        Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 4/4] mm, notifier: Catch sleeping/blocking for !blockable
Message-ID: <20190821161635.GC8653@ziepe.ca>
References: <20190820081902.24815-1-daniel.vetter@ffwll.ch>
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 <20190820133418.GG29246@ziepe.ca>
 <20190820151810.GG11147@phenom.ffwll.local>
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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