From: John Hubbard <jhubbard@nvidia.com>
To: jglisse@redhat.com, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
Evgeny Baskakov <ebaskakov@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Mark Hairgrove <mhairgrove@nvidia.com>
Subject: Re: [PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit v2
Date: Wed, 21 Mar 2018 16:22:49 -0700 [thread overview]
Message-ID: <a9ba54c5-a2d9-49f6-16ad-46b79525b93c@nvidia.com> (raw)
In-Reply-To: <20180321181614.9968-1-jglisse@redhat.com>
On 03/21/2018 11:16 AM, jglisse@redhat.com wrote:
> From: Jérôme Glisse <jglisse@redhat.com>
>
> This code was lost in translation at one point. This properly call
> mmu_notifier_unregister_no_release() once last user is gone. This
> fix the zombie mm_struct as without this patch we do not drop the
> refcount we have on it.
>
> Changed since v1:
> - close race window between a last mirror unregistering and a new
> mirror registering, which could have lead to use after free()
> kind of bug
>
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> Cc: Mark Hairgrove <mhairgrove@nvidia.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> ---
> mm/hmm.c | 35 +++++++++++++++++++++++++++++++++--
> 1 file changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 6088fa6ed137..f75aa8df6e97 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -222,13 +222,24 @@ int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
> if (!mm || !mirror || !mirror->ops)
> return -EINVAL;
>
> +again:
> mirror->hmm = hmm_register(mm);
> if (!mirror->hmm)
> return -ENOMEM;
>
> down_write(&mirror->hmm->mirrors_sem);
> - list_add(&mirror->list, &mirror->hmm->mirrors);
> - up_write(&mirror->hmm->mirrors_sem);
> + if (mirror->hmm->mm == NULL) {
> + /*
> + * A racing hmm_mirror_unregister() is about to destroy the hmm
> + * struct. Try again to allocate a new one.
> + */
> + up_write(&mirror->hmm->mirrors_sem);
> + mirror->hmm = NULL;
This is being set outside of locks, so now there is another race with
another hmm_mirror_register...
I'll take a moment and draft up what I have in mind here, which is a more
symmetrical locking scheme for these routines.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2018-03-21 23:22 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-20 2:00 [PATCH 00/15] hmm: fixes and documentations v3 jglisse
2018-03-20 2:00 ` [PATCH 01/15] mm/hmm: documentation editorial update to HMM documentation jglisse
2018-03-20 2:00 ` [PATCH 02/15] mm/hmm: fix header file if/else/endif maze v2 jglisse
2018-03-20 2:00 ` [PATCH 03/15] mm/hmm: HMM should have a callback before MM is destroyed v2 jglisse
2018-03-21 4:14 ` John Hubbard
2018-03-21 18:03 ` Jerome Glisse
2018-03-21 22:16 ` John Hubbard
2018-03-21 22:46 ` Jerome Glisse
2018-03-21 23:10 ` John Hubbard
2018-03-21 23:37 ` Jerome Glisse
2018-03-22 0:11 ` John Hubbard
2018-03-22 1:32 ` Jerome Glisse
2018-03-22 1:28 ` [PATCH 03/15] mm/hmm: HMM should have a callback before MM is destroyed v3 jglisse
2018-03-22 6:58 ` John Hubbard
2018-03-20 2:00 ` [PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit jglisse
2018-03-21 4:24 ` John Hubbard
2018-03-21 18:12 ` Jerome Glisse
2018-03-21 18:16 ` [PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit v2 jglisse
2018-03-21 23:22 ` John Hubbard [this message]
2018-03-21 23:41 ` Jerome Glisse
2018-03-22 22:47 ` John Hubbard
2018-03-22 23:37 ` Jerome Glisse
2018-03-23 0:13 ` John Hubbard
2018-03-23 0:50 ` Jerome Glisse
2018-03-23 0:56 ` John Hubbard
2018-03-22 1:30 ` [PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit v3 jglisse
2018-03-22 22:36 ` Andrew Morton
2018-03-20 2:00 ` [PATCH 05/15] mm/hmm: hmm_pfns_bad() was accessing wrong struct jglisse
2018-03-20 2:00 ` [PATCH 06/15] mm/hmm: use struct for hmm_vma_fault(), hmm_vma_get_pfns() parameters v2 jglisse
2018-03-20 2:00 ` [PATCH 07/15] mm/hmm: remove HMM_PFN_READ flag and ignore peculiar architecture v2 jglisse
2018-03-20 2:00 ` [PATCH 08/15] mm/hmm: use uint64_t for HMM pfn instead of defining hmm_pfn_t to ulong v2 jglisse
2018-03-20 2:00 ` [PATCH 09/15] mm/hmm: cleanup special vma handling (VM_SPECIAL) jglisse
2018-03-20 2:00 ` [PATCH 10/15] mm/hmm: do not differentiate between empty entry or missing directory v2 jglisse
2018-03-21 5:24 ` John Hubbard
2018-03-21 14:48 ` Jerome Glisse
2018-03-21 23:16 ` John Hubbard
2018-03-20 2:00 ` [PATCH 11/15] mm/hmm: rename HMM_PFN_DEVICE_UNADDRESSABLE to HMM_PFN_DEVICE_PRIVATE jglisse
2018-03-20 2:00 ` [PATCH 12/15] mm/hmm: move hmm_pfns_clear() closer to where it is use jglisse
2018-03-20 2:00 ` [PATCH 13/15] mm/hmm: factor out pte and pmd handling to simplify hmm_vma_walk_pmd() jglisse
2018-03-21 5:07 ` John Hubbard
2018-03-21 15:08 ` Jerome Glisse
2018-03-21 22:36 ` John Hubbard
2018-03-20 2:00 ` [PATCH 14/15] mm/hmm: change hmm_vma_fault() to allow write fault on page basis jglisse
2018-03-20 2:00 ` [PATCH 15/15] mm/hmm: use device driver encoding for HMM pfn v2 jglisse
2018-03-21 4:39 ` John Hubbard
2018-03-21 15:52 ` Jerome Glisse
2018-03-21 23:19 ` John Hubbard
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