[PATCH 3.11 148/208] mm: numa: ensure anon_vma is locked to prevent parallel THP splits

[Luis Henriques]

3.11.10.3 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mel Gorman <mgorman at suse.de>

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 at suse.de>
Reviewed-by: Rik van Riel <riel at redhat.com>
Cc: Alex Thorlton <athorlton at sgi.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 mm/huge_memory.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ac2546c..0db1517 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1354,6 +1354,13 @@ 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.
-- 
1.8.3.2