Re: [PATCH v2 5/6] mm: hugetlb: fix a race between isolating and freeing page

2021-01-06 Thread Michal Hocko 
On Wed 06-01-21 16:47:38, Muchun Song wrote:
> There is a race between isolate_huge_page() and __free_huge_page().
> 
> CPU0:   CPU1:
> 
> if (PageHuge(page))
> put_page(page)
>   __free_huge_page(page)
>   spin_lock(_lock)
>   update_and_free_page(page)
> 
> set_compound_page_dtor(page,
>   NULL_COMPOUND_DTOR)
>   spin_unlock(_lock)
>   isolate_huge_page(page)
> // trigger BUG_ON
> VM_BUG_ON_PAGE(!PageHead(page), page)
> spin_lock(_lock)
> page_huge_active(page)
>   // trigger BUG_ON
>   VM_BUG_ON_PAGE(!PageHuge(page), page)
> spin_unlock(_lock)
> 
> When we isolate a HugeTLB page on CPU0. Meanwhile, we free it to the
> buddy allocator on CPU1. Then, we can trigger a BUG_ON on CPU0. Because
> it is already freed to the buddy allocator.
> 
> Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle 
> hugepage")
> Signed-off-by: Muchun Song 
> Reviewed-by: Mike Kravetz 

Acked-by: Michal Hocko 

Thanks!
> ---
>  mm/hugetlb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bf02e81e3953..67200dd25b1d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5587,9 +5587,9 @@ bool isolate_huge_page(struct page *page, struct 
> list_head *list)
>  {
>   bool ret = true;
>  
> - VM_BUG_ON_PAGE(!PageHead(page), page);
>   spin_lock(_lock);
> - if (!page_huge_active(page) || !get_page_unless_zero(page)) {
> + if (!PageHeadHuge(page) || !page_huge_active(page) ||
> + !get_page_unless_zero(page)) {
>   ret = false;
>   goto unlock;
>   }
> -- 
> 2.11.0

-- 
Michal Hocko
SUSE Labs

[PATCH v2 5/6] mm: hugetlb: fix a race between isolating and freeing page

2021-01-06 Thread Muchun Song 
There is a race between isolate_huge_page() and __free_huge_page().

CPU0:   CPU1:

if (PageHuge(page))
put_page(page)
  __free_huge_page(page)
  spin_lock(_lock)
  update_and_free_page(page)
set_compound_page_dtor(page,
  NULL_COMPOUND_DTOR)
  spin_unlock(_lock)
  isolate_huge_page(page)
// trigger BUG_ON
VM_BUG_ON_PAGE(!PageHead(page), page)
spin_lock(_lock)
page_huge_active(page)
  // trigger BUG_ON
  VM_BUG_ON_PAGE(!PageHuge(page), page)
spin_unlock(_lock)

When we isolate a HugeTLB page on CPU0. Meanwhile, we free it to the
buddy allocator on CPU1. Then, we can trigger a BUG_ON on CPU0. Because
it is already freed to the buddy allocator.

Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle 
hugepage")
Signed-off-by: Muchun Song 
Reviewed-by: Mike Kravetz 
---
 mm/hugetlb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index bf02e81e3953..67200dd25b1d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5587,9 +5587,9 @@ bool isolate_huge_page(struct page *page, struct 
list_head *list)
 {
bool ret = true;
 
-   VM_BUG_ON_PAGE(!PageHead(page), page);
spin_lock(_lock);
-   if (!page_huge_active(page) || !get_page_unless_zero(page)) {
+   if (!PageHeadHuge(page) || !page_huge_active(page) ||
+   !get_page_unless_zero(page)) {
ret = false;
goto unlock;
}
-- 
2.11.0