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,
Ralph Campbell <rcampbell@nvidia.com>,
stable@vger.kernel.org, Evgeny Baskakov <ebaskakov@nvidia.com>,
Mark Hairgrove <mhairgrove@nvidia.com>
Subject: Re: [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2
Date: Fri, 16 Mar 2018 21:39:00 -0700 [thread overview]
Message-ID: <b1406b15-858f-00a2-e2c1-a950d190f0e1@nvidia.com> (raw)
In-Reply-To: <b0cd570b-dfe4-4b42-18bb-967d1dbddcb3@nvidia.com>
On 03/16/2018 08:47 PM, John Hubbard wrote:
> On 03/16/2018 07:36 PM, John Hubbard wrote:
>> On 03/16/2018 12:14 PM, jglisse@redhat.com wrote:
>>> From: Ralph Campbell <rcampbell@nvidia.com>
>>>
>>
>> <snip>
>>
>>> +static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
>>> +{
>>> + struct hmm *hmm = mm->hmm;
>>> + struct hmm_mirror *mirror;
>>> + struct hmm_mirror *mirror_next;
>>> +
>>> + down_write(&hmm->mirrors_sem);
>>> + list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) {
>>> + list_del_init(&mirror->list);
>>> + if (mirror->ops->release)
>>> + mirror->ops->release(mirror);
>>> + }
>>> + up_write(&hmm->mirrors_sem);
>>> +}
>>> +
>>
>> OK, as for actual code review:
>>
>> This part of the locking looks good. However, I think it can race against
>> hmm_mirror_register(), because hmm_mirror_register() will just add a new
>> mirror regardless.
>>
>> So:
>>
>> thread 1 thread 2
>> -------------- -----------------
>> hmm_release hmm_mirror_register
>> down_write(&hmm->mirrors_sem); <blocked: waiting for sem>
>> // deletes all list items
>> up_write
>> unblocked: adds new mirror
>>
>>
Mark Hairgrove just pointed out some more fun facts:
1. Because hmm_mirror_register() needs to be called with an mm that has a non-zero
refcount, you generally cannot get an hmm_release callback, so the above race should
not happen.
2. We looked around, and the code is missing a call to mmu_notifier_unregister().
That means that it is going to leak memory and not let the mm get released either.
Maybe having each mirror have its own mmu notifier callback is a possible way
to solve this.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2018-03-17 4:39 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-16 19:14 [PATCH 0/4] hmm: fixes and documentations v2 jglisse
2018-03-16 19:14 ` [PATCH 01/14] mm/hmm: documentation editorial update to HMM documentation jglisse
2018-03-16 19:14 ` [PATCH 02/14] mm/hmm: fix header file if/else/endif maze jglisse
2018-03-16 21:09 ` Andrew Morton
2018-03-16 21:18 ` Jerome Glisse
2018-03-16 21:35 ` Andrew Morton
2018-03-16 21:40 ` John Hubbard
2018-03-17 1:20 ` [PATCH 02/14] mm/hmm: fix header file if/else/endif maze v2 jglisse
2018-03-16 19:14 ` [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2 jglisse
2018-03-16 21:12 ` Andrew Morton
2018-03-16 21:26 ` Jerome Glisse
2018-03-16 21:37 ` John Hubbard
2018-03-17 2:36 ` John Hubbard
2018-03-17 3:47 ` John Hubbard
2018-03-17 4:39 ` John Hubbard [this message]
2018-03-16 19:14 ` [PATCH 04/14] mm/hmm: hmm_pfns_bad() was accessing wrong struct jglisse
2018-03-17 2:04 ` John Hubbard
2018-03-16 19:14 ` [PATCH 05/14] mm/hmm: use struct for hmm_vma_fault(), hmm_vma_get_pfns() parameters jglisse
2018-03-17 3:08 ` John Hubbard
2018-03-16 19:14 ` [PATCH 06/14] mm/hmm: remove HMM_PFN_READ flag and ignore peculiar architecture jglisse
2018-03-17 3:30 ` John Hubbard
2018-03-16 19:14 ` [PATCH 07/14] mm/hmm: use uint64_t for HMM pfn instead of defining hmm_pfn_t to ulong jglisse
2018-03-17 3:59 ` John Hubbard
2018-03-16 19:14 ` [PATCH 08/14] mm/hmm: cleanup special vma handling (VM_SPECIAL) jglisse
2018-03-17 4:35 ` John Hubbard
2018-03-16 19:14 ` [PATCH 09/14] mm/hmm: do not differentiate between empty entry or missing directory jglisse
2018-03-19 23:06 ` John Hubbard
2018-03-20 2:08 ` Jerome Glisse
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