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From: Jason Gunthorpe <jgg@ziepe.ca>
To: linux-rdma@vger.kernel.org, linux-mm@kvack.org,
	Jerome Glisse <jglisse@redhat.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	John Hubbard <jhubbard@nvidia.com>
Subject: Re: [RFC PATCH 00/11] mm/hmm: Various revisions from a locking/code review
Date: Fri, 24 May 2019 11:36:49 -0300	[thread overview]
Message-ID: <20190524143649.GA14258@ziepe.ca> (raw)
In-Reply-To: <20190523153436.19102-1-jgg@ziepe.ca>

On Thu, May 23, 2019 at 12:34:25PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> This patch series arised out of discussions with Jerome when looking at the
> ODP changes, particularly informed by use after free races we have already
> found and fixed in the ODP code (thanks to syzkaller) working with mmu
> notifiers, and the discussion with Ralph on how to resolve the lifetime model.

So the last big difference with ODP's flow is how 'range->valid'
works.

In ODP this was done using the rwsem umem->umem_rwsem which is
obtained for read in invalidate_start and released in invalidate_end.

Then any other threads that wish to only work on a umem which is not
undergoing invalidation will obtain the write side of the lock, and
within that lock's critical section the virtual address range is known
to not be invalidating.

I cannot understand how hmm gets to the same approach. It has
range->valid, but it is not locked by anything that I can see, so when
we test it in places like hmm_range_fault it seems useless..

Jerome, how does this work?

I have a feeling we should copy the approach from ODP and use an
actual lock here.

Jason


  parent reply	other threads:[~2019-05-24 14:36 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-23 15:34 [RFC PATCH 00/11] mm/hmm: Various revisions from a locking/code review Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 01/11] mm/hmm: Fix use after free with struct hmm in the mmu notifiers Jason Gunthorpe
2019-06-06 23:54   ` Ira Weiny
2019-06-07 14:17     ` Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 02/11] mm/hmm: Use hmm_mirror not mm as an argument for hmm_register_range Jason Gunthorpe
2019-05-23 18:22   ` Christoph Hellwig
2019-05-23 15:34 ` [RFC PATCH 03/11] mm/hmm: Hold a mmgrab from hmm to mm Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 04/11] mm/hmm: Simplify hmm_get_or_create and make it reliable Jason Gunthorpe
2019-05-23 23:38   ` Ralph Campbell
2019-05-24  1:23     ` Jason Gunthorpe
2019-05-24 17:06       ` Ralph Campbell
2019-05-23 15:34 ` [RFC PATCH 05/11] mm/hmm: Improve locking around hmm->dead Jason Gunthorpe
2019-05-24 13:40   ` Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 06/11] mm/hmm: Remove duplicate condition test before wait_event_timeout Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 07/11] mm/hmm: Delete hmm_mirror_mm_is_alive() Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 08/11] mm/hmm: Use lockdep instead of comments Jason Gunthorpe
2019-06-07 19:33   ` Souptick Joarder
2019-06-07 19:39     ` Jason Gunthorpe
2019-06-07 21:02       ` Souptick Joarder
2019-06-08  1:15         ` Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 09/11] mm/hmm: Remove racy protection against double-unregistration Jason Gunthorpe
2019-06-07 19:38   ` Souptick Joarder
2019-06-07 19:37     ` Jason Gunthorpe
2019-06-07 19:55       ` Souptick Joarder
2019-05-23 15:34 ` [RFC PATCH 10/11] mm/hmm: Poison hmm_range during unregister Jason Gunthorpe
2019-06-07 20:13   ` Souptick Joarder
2019-06-07 20:18     ` Jason Gunthorpe
2019-05-23 15:34 ` [RFC PATCH 11/11] mm/hmm: Do not use list*_rcu() for hmm->ranges Jason Gunthorpe
2019-06-07 20:22   ` Souptick Joarder
2019-05-23 19:04 ` [RFC PATCH 00/11] mm/hmm: Various revisions from a locking/code review John Hubbard
2019-05-23 19:37   ` Jason Gunthorpe
2019-05-23 20:59   ` Jerome Glisse
2019-05-24 13:35 ` Jason Gunthorpe
2019-05-24 14:36 ` Jason Gunthorpe [this message]
2019-05-24 16:49   ` Jerome Glisse
2019-05-24 16:59     ` Jason Gunthorpe
2019-05-24 17:01       ` Jerome Glisse
2019-05-24 17:52         ` Jason Gunthorpe
2019-05-24 18:03           ` Jerome Glisse
2019-05-24 18:32             ` Jason Gunthorpe
2019-05-24 18:46               ` Jerome Glisse
2019-05-24 22:09                 ` Jason Gunthorpe
2019-05-27 19:58                   ` Jason Gunthorpe
2019-05-24 17:47     ` Ralph Campbell
2019-05-24 17:51       ` Jerome Glisse

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