mm: numa: ensure anon_vma is locked to prevent parallel THP splits

commit c3a489cac38d43ea6dc4ac240473b44b46deecf7 upstream.

The anon_vma lock prevents parallel THP splits and any associated
complexity that arises when handling splits during THP migration.  This
patch checks if the lock was successfully acquired and bails from THP
migration if it failed for any reason.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Alex Thorlton <athorlton@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c403a74e4bee..b2e803e14ea9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1344,6 +1344,13 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 goto out_unlock;
         }
 
+        /* Bail if we fail to protect against THP splits for any reason */
+        if (unlikely(!anon_vma)) {
+                put_page(page);
+                page_nid = -1;
+                goto clear_pmdnuma;
+        }
+
         /*
          * Migrate the THP to the requested node, returns with page unlocked
          * and pmd_numa cleared.