hugetlb: clarify hugetlb_instantiation_mutex usage
authorMichal Hocko <mhocko@suse.cz>
Tue, 10 Jan 2012 23:07:21 +0000 (15:07 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 11 Jan 2012 00:30:42 +0000 (16:30 -0800)
Let's make it clear that we cannot race with other fault handlers due to
hugetlb (global) mutex.  Also make it clear that we want to keep pte_same
checks anayway to have a transition from the global mutex easier.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/hugetlb.c

index 2c551b28ba69c655608d746905fd42f60924708c..49e693b7fd0c695aeced27be87ab7ed0ae98e8d0 100644 (file)
@@ -2349,6 +2349,9 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
 
 /*
  * Hugetlb_cow() should be called with page lock of the original hugepage held.
+ * Called with hugetlb_instantiation_mutex held and pte_page locked so we
+ * cannot race with other handlers or page migration.
+ * Keep the pte_same checks anyway to make transition from the mutex easier.
  */
 static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
                        unsigned long address, pte_t *ptep, pte_t pte,