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From: Souptick Joarder <jrdr.linux@gmail.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-rdma@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
	 Jerome Glisse <jglisse@redhat.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	 John Hubbard <jhubbard@nvidia.com>,
	Jason Gunthorpe <jgg@mellanox.com>
Subject: Re: [RFC PATCH 09/11] mm/hmm: Remove racy protection against double-unregistration
Date: Sat, 8 Jun 2019 01:08:37 +0530	[thread overview]
Message-ID: <CAFqt6zarGTZeA+Dw_RT2WXwgoYhnKP28LGfc+CDZqNFRexEXoQ@mail.gmail.com> (raw)
In-Reply-To: <20190523153436.19102-10-jgg@ziepe.ca>

On Thu, May 23, 2019 at 9:05 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> From: Jason Gunthorpe <jgg@mellanox.com>
>
> No other register/unregister kernel API attempts to provide this kind of
> protection as it is inherently racy, so just drop it.
>
> Callers should provide their own protection, it appears nouveau already
> does, but just in case drop a debugging POISON.
>
> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
> ---
>  mm/hmm.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 46872306f922bb..6c3b7398672c29 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -286,18 +286,13 @@ EXPORT_SYMBOL(hmm_mirror_register);
>   */
>  void hmm_mirror_unregister(struct hmm_mirror *mirror)
>  {
> -       struct hmm *hmm = READ_ONCE(mirror->hmm);
> -
> -       if (hmm == NULL)
> -               return;
> +       struct hmm *hmm = mirror->hmm;

How about remove struct hmm *hmm and replace the code like below -

down_write(&mirror->hmm->mirrors_sem);
list_del_init(&mirror->list);
up_write(&mirror->hmm->mirrors_sem);
hmm_put(hmm);
memset(&mirror->hmm, POISON_INUSE, sizeof(mirror->hmm));

Similar to hmm_mirror_register().


>         down_write(&hmm->mirrors_sem);
>         list_del_init(&mirror->list);
> -       /* To protect us against double unregister ... */
> -       mirror->hmm = NULL;
>         up_write(&hmm->mirrors_sem);
> -
>         hmm_put(hmm);
> +       memset(&mirror->hmm, POISON_INUSE, sizeof(mirror->hmm));
>  }
>  EXPORT_SYMBOL(hmm_mirror_unregister);
>
> --
> 2.21.0
>


  reply	other threads:[~2019-06-07 19:33 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 [this message]
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
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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