The patch titled
Subject: mm/hugetlb: use get_page_unless_zero() in hugetlb_fault()
has been removed from the -mm tree. Its filename was
mm-hugetlb-use-get_page_unless_zero-in-hugetlb_fault.patch
This patch was dropped because an updated version will be merged
------------------------------------------------------
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Subject: mm/hugetlb: use get_page_unless_zero() in hugetlb_fault()
After fixing locking in follow_page(FOLL_GET) for hugepages, I start to
observe the BUG of "get_page() on refcount 0 page" in hugetlb_fault() in
the same test.
I'm not exactly sure about how this race is triggered, but hugetlb_fault()
calls pte_page() and get_page() outside page table lock, so it's not safe.
This patch checks the refcount of the gotten page, and aborts the page
fault if the refcount is 0, expecting to retry.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [3.12+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff -puN mm/hugetlb.c~mm-hugetlb-use-get_page_unless_zero-in-hugetlb_fault mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-use-get_page_unless_zero-in-hugetlb_fault
+++ a/mm/hugetlb.c
@@ -3192,7 +3192,8 @@ int hugetlb_fault(struct mm_struct *mm,
* so no worry about deadlock.
*/
page = pte_page(entry);
- get_page(page);
+ if (!get_page_unless_zero(page))
+ goto out_put_pagecache;
if (page != pagecache_page)
lock_page(page);
@@ -3218,15 +3219,14 @@ int hugetlb_fault(struct mm_struct *mm,
out_ptl:
spin_unlock(ptl);
-
+ if (page != pagecache_page)
+ unlock_page(page);
+ put_page(page);
+out_put_pagecache:
if (pagecache_page) {
unlock_page(pagecache_page);
put_page(pagecache_page);
}
- if (page != pagecache_page)
- unlock_page(page);
- put_page(page);
-
out_mutex:
mutex_unlock(&htlb_fault_mutex_table[hash]);
return ret;
_
Patches currently in -mm which might be from n-horiguchi@xxxxxxxxxxxxx are
origin.patch
memory-hotplug-add-sysfs-zones_online_to-attribute.patch
mm-hugetlb-add-migration-entry-check-in-hugetlb_change_protection.patch
mm-hugetlb-remove-unused-argument-of-follow_huge_pmdpud.patch
mm-introduce-do_shared_fault-and-drop-do_fault-fix-fix.patch
do_shared_fault-check-that-mmap_sem-is-held.patch
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