mm, rmap: fix false positive VM_BUG() in page_add_file_rmap()
PageTransCompound() doesn't distinguish THP from from any other type of
compound pages. This can lead to false-positive VM_BUG_ON() in
page_add_file_rmap() if called on compound page from a driver[1].
I think we can exclude such cases by checking if the page belong to a
mapping.
The VM_BUG_ON_PAGE() is downgraded to VM_WARN_ON_ONCE(). This path
should not cause any harm to non-THP page, but good to know if we step
on anything else.
[1] http://lkml.kernel.org/r/c711e067-0bff-a6cb-3c37-04dfe77d2db1@redhat.com
Link: http://lkml.kernel.org/r/20160810161345.GA67522@black.fi.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Laura Abbott <labbott@redhat.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/rmap.c b/mm/rmap.c
index 709bc83..d4f5606 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1284,8 +1284,9 @@
VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
__inc_node_page_state(page, NR_SHMEM_PMDMAPPED);
} else {
- if (PageTransCompound(page)) {
- VM_BUG_ON_PAGE(!PageLocked(page), page);
+ if (PageTransCompound(page) && page_mapping(page)) {
+ VM_WARN_ON_ONCE(!PageLocked(page));
+
SetPageDoubleMap(compound_head(page));
if (PageMlocked(page))
clear_page_mlock(compound_head(page));