From: Mike Kravetz <mike.kravetz@oracle.com>
To: Michal Hocko <mhocko@suse.com>, Muchun Song <songmuchun@bytedance.com>
Cc: akpm@linux-foundation.org, n-horiguchi@ah.jp.nec.com,
ak@linux.intel.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page
Date: Wed, 6 Jan 2021 12:58:29 -0800 [thread overview]
Message-ID: <a9c59b0e-9a9d-c568-5503-5df6fe8db908@oracle.com> (raw)
In-Reply-To: <20210106165632.GT13207@dhcp22.suse.cz>
On 1/6/21 8:56 AM, Michal Hocko wrote:
> On Wed 06-01-21 16:47:36, Muchun Song wrote:
>> There is a race condition between __free_huge_page()
>> and dissolve_free_huge_page().
>>
>> CPU0: CPU1:
>>
>> // page_count(page) == 1
>> put_page(page)
>> __free_huge_page(page)
>> dissolve_free_huge_page(page)
>> spin_lock(&hugetlb_lock)
>> // PageHuge(page) && !page_count(page)
>> update_and_free_page(page)
>> // page is freed to the buddy
>> spin_unlock(&hugetlb_lock)
>> spin_lock(&hugetlb_lock)
>> clear_page_huge_active(page)
>> enqueue_huge_page(page)
>> // It is wrong, the page is already freed
>> spin_unlock(&hugetlb_lock)
>>
>> The race windows is between put_page() and spin_lock() which
>> is in the __free_huge_page().
>
> The race window reall is between put_page and dissolve_free_huge_page.
> And the result is that the put_page path would clobber an unrelated page
> (either free or already reused page) which is quite serious.
> Fortunatelly pages are dissolved very rarely. I believe that user would
> require to be privileged to hit this by intention.
>
>> We should make sure that the page is already on the free list
>> when it is dissolved.
>
> Another option would be to check for PageHuge in __free_huge_page. Have
> you considered that rather than add yet another state? The scope of the
> spinlock would have to be extended. If that sounds more tricky then can
> we check the page->lru in the dissolve path? If the page is still
> PageHuge and reference count 0 then there shouldn't be many options
> where it can be queued, right?
The tricky part with expanding lock scope will be the potential call to
hugepage_subpool_put_pages as it may also try to acquire the hugetlb_lock.
I am not sure what you mean by 'check the page->lru'? If we knew the page
was on the free list, then we could dissolve. But, I do not think there
is an easy way to determine that from page->lru. A hugetlb page is either
going to be on the active list or free list.
>
>> Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> ---
>> mm/hugetlb.c | 38 ++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 38 insertions(+)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 4741d60f8955..8ff138c17129 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -79,6 +79,21 @@ DEFINE_SPINLOCK(hugetlb_lock);
>> static int num_fault_mutexes;
>> struct mutex *hugetlb_fault_mutex_table ____cacheline_aligned_in_smp;
>>
>> +static inline bool PageHugeFreed(struct page *head)
>> +{
>> + return (unsigned long)head[3].mapping == -1U;
>> +}
>> +
>> +static inline void SetPageHugeFreed(struct page *head)
>> +{
>> + head[3].mapping = (void *)-1U;
>> +}
>> +
>> +static inline void ClearPageHugeFreed(struct page *head)
>> +{
>> + head[3].mapping = NULL;
>> +}
>> +
>> /* Forward declaration */
>> static int hugetlb_acct_memory(struct hstate *h, long delta);
>>
>> @@ -1028,6 +1043,7 @@ static void enqueue_huge_page(struct hstate *h, struct page *page)
>> list_move(&page->lru, &h->hugepage_freelists[nid]);
>> h->free_huge_pages++;
>> h->free_huge_pages_node[nid]++;
>> + SetPageHugeFreed(page);
>> }
>>
>> static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
>> @@ -1044,6 +1060,7 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
>>
>> list_move(&page->lru, &h->hugepage_activelist);
>> set_page_refcounted(page);
>> + ClearPageHugeFreed(page);
>> h->free_huge_pages--;
>> h->free_huge_pages_node[nid]--;
>> return page;
>> @@ -1291,6 +1308,17 @@ static inline void destroy_compound_gigantic_page(struct page *page,
>> unsigned int order) { }
>> #endif
>>
>> +/*
>> + * Because we reuse the mapping field of some tail page structs, we should
>> + * reset those mapping to initial value before @head is freed to the buddy
>> + * allocator. The invalid value will be checked in the free_tail_pages_check().
>> + */
When I suggested using head[3].mapping for this state, I was not aware of
this requirement. My suggestion was only following the convention used in
PageHugeTemporary. I would not have made the suggestion if I had realized
this was required. Sorry.
--
Mike Kravetz
>> +static inline void reset_tail_page_mapping(struct hstate *h, struct page *head)
>> +{
>> + if (!hstate_is_gigantic(h))
>> + head[3].mapping = TAIL_MAPPING;
>> +}
>> +
>> static void update_and_free_page(struct hstate *h, struct page *page)
>> {
>> int i;
>> @@ -1298,6 +1326,7 @@ static void update_and_free_page(struct hstate *h, struct page *page)
>> if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
>> return;
>>
>> + reset_tail_page_mapping(h, page);
>> h->nr_huge_pages--;
>> h->nr_huge_pages_node[page_to_nid(page)]--;
>> for (i = 0; i < pages_per_huge_page(h); i++) {
>> @@ -1504,6 +1533,7 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
>> spin_lock(&hugetlb_lock);
>> h->nr_huge_pages++;
>> h->nr_huge_pages_node[nid]++;
>> + ClearPageHugeFreed(page);
>> spin_unlock(&hugetlb_lock);
>> }
>>
>> @@ -1770,6 +1800,14 @@ int dissolve_free_huge_page(struct page *page)
>> int nid = page_to_nid(head);
>> if (h->free_huge_pages - h->resv_huge_pages == 0)
>> goto out;
>> +
>> + /*
>> + * We should make sure that the page is already on the free list
>> + * when it is dissolved.
>> + */
>> + if (unlikely(!PageHugeFreed(head)))
>> + goto out;
>> +
>> /*
>> * Move PageHWPoison flag from head page to the raw error page,
>> * which makes any subpages rather than the error page reusable.
>> --
>> 2.11.0
>
next prev parent reply other threads:[~2021-01-06 21:00 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 8:47 [PATCH v2 0/6] Fix some bugs about HugeTLB code Muchun Song
2021-01-06 8:47 ` [PATCH v2 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one Muchun Song
2021-01-06 16:13 ` Michal Hocko
2021-01-07 2:52 ` [External] " Muchun Song
2021-01-07 11:16 ` Michal Hocko
2021-01-07 11:24 ` Muchun Song
2021-01-07 11:48 ` Michal Hocko
2021-01-06 8:47 ` [PATCH v2 2/6] mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page Muchun Song
2021-01-06 16:35 ` Michal Hocko
2021-01-06 19:30 ` Mike Kravetz
2021-01-06 20:02 ` Michal Hocko
2021-01-06 21:07 ` Mike Kravetz
2021-01-07 8:36 ` Michal Hocko
2021-01-07 2:58 ` [External] " Muchun Song
2021-01-06 8:47 ` [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page Muchun Song
2021-01-06 16:56 ` Michal Hocko
2021-01-06 20:58 ` Mike Kravetz [this message]
2021-01-07 3:08 ` [External] " Muchun Song
2021-01-07 8:40 ` Michal Hocko
2021-01-08 0:52 ` Mike Kravetz
2021-01-08 8:28 ` Michal Hocko
2021-01-07 5:39 ` [External] " Muchun Song
2021-01-07 8:41 ` Michal Hocko
2021-01-07 8:53 ` Muchun Song
2021-01-07 11:18 ` Michal Hocko
2021-01-07 11:38 ` Muchun Song
2021-01-07 12:38 ` Michal Hocko
2021-01-07 12:59 ` Muchun Song
2021-01-07 14:11 ` Michal Hocko
2021-01-07 15:11 ` Muchun Song
2021-01-08 1:06 ` Mike Kravetz
2021-01-08 2:38 ` Muchun Song
2021-01-08 8:43 ` Michal Hocko
2021-01-08 9:01 ` Muchun Song
2021-01-08 9:31 ` Michal Hocko
2021-01-08 10:08 ` Muchun Song
2021-01-08 11:44 ` Michal Hocko
2021-01-08 11:52 ` Muchun Song
2021-01-08 12:04 ` Michal Hocko
2021-01-08 12:24 ` Muchun Song
2021-01-06 8:47 ` [PATCH v2 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge_page Muchun Song
2021-01-06 17:07 ` Michal Hocko
2021-01-07 3:11 ` [External] " Muchun Song
2021-01-07 8:39 ` Michal Hocko
2021-01-07 9:01 ` Muchun Song
2021-01-07 11:22 ` Michal Hocko
2021-01-06 8:47 ` [PATCH v2 5/6] mm: hugetlb: fix a race between isolating and freeing page Muchun Song
2021-01-06 17:10 ` Michal Hocko
2021-01-06 8:47 ` [PATCH v2 6/6] mm: hugetlb: remove VM_BUG_ON_PAGE from page_huge_active Muchun Song
2021-01-06 17:16 ` Michal Hocko
2021-01-08 22:24 ` Mike Kravetz
2021-01-09 4:07 ` [External] " Muchun Song
2021-01-07 9:30 ` [PATCH v2 0/6] Fix some bugs about HugeTLB code David Hildenbrand
2021-01-07 9:40 ` [External] " Muchun Song
2021-01-07 10:10 ` David Hildenbrand
2021-01-07 10:16 ` Muchun Song
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=a9c59b0e-9a9d-c568-5503-5df6fe8db908@oracle.com \
--to=mike.kravetz@oracle.com \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=n-horiguchi@ah.jp.nec.com \
--cc=songmuchun@bytedance.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).