The patch titled
Subject: mm, rmap: fix false positive VM_BUG() in page_add_file_rmap()
has been added to the -mm tree. Its filename is
mm-rmap-fix-false-positive-vm_bug-in-page_add_file_rmap.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-rmap-fix-false-positive-vm_bug-in-page_add_file_rmap.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-rmap-fix-false-positive-vm_bug-in-page_add_file_rmap.patch
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From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20160810161345.GA67522@xxxxxxxxxxxxxxxxxx
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Laura Abbott <labbott@xxxxxxxxxx>
Tested-by: Laura Abbott <labbott@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -puN mm/rmap.c~mm-rmap-fix-false-positive-vm_bug-in-page_add_file_rmap mm/rmap.c
--- a/mm/rmap.c~mm-rmap-fix-false-positive-vm_bug-in-page_add_file_rmap
+++ a/mm/rmap.c
@@ -1284,8 +1284,9 @@ void page_add_file_rmap(struct page *pag
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));
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mm-rmap-fix-false-positive-vm_bug-in-page_add_file_rmap.patch
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