[PATCH 4.4 023/131] mm/rmap: replace BUG_ON(anon_vma->degree) with VM_WARN_ON

[Greg Kroah-Hartman]

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

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

From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>

commit e4c5800a3991f0c6a766983535dfc10d51802cf6 upstream.

This check effectively catches anon vma hierarchy inconsistence and some
vma corruptions.  It was effective for catching corner cases in anon vma
reusing logic.  For now this code seems stable so check could be hidden
under CONFIG_DEBUG_VM and replaced with WARN because it's not so fatal.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Suggested-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/rmap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -408,7 +408,7 @@ void unlink_anon_vmas(struct vm_area_str
 	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
 		struct anon_vma *anon_vma = avc->anon_vma;
 
-		BUG_ON(anon_vma->degree);
+		VM_WARN_ON(anon_vma->degree);
 		put_anon_vma(anon_vma);
 
 		list_del(&avc->same_vma);