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Subject[PATCH v4] kpageflags: fix wrong KPF_THP on non-huge compound pages
Date
KPF_THP can be set on non-huge compound pages (like slab pages or pages
allocated by drivers with __GFP_COMP) because PageTransCompound only
checks PG_head and PG_tail. Obviously this is a bug and breaks user space
applications which look for thp via /proc/kpageflags.

This patch rules out setting KPF_THP wrongly by additionally checking
PageLRU on the head pages.

Changelog in v4:
- check PageLRU with compound_trans_head()
- fix patch subject again

Changelog in v3:
- check PageSlab instead of PageAnon
- fix patch subject

Changelog in v2:
- add a comment in code

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
---
fs/proc/page.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git v3.6-rc6.orig/fs/proc/page.c v3.6-rc6/fs/proc/page.c
index 7fcd0d6..b8730d9 100644
--- v3.6-rc6.orig/fs/proc/page.c
+++ v3.6-rc6/fs/proc/page.c
@@ -115,7 +115,13 @@ u64 stable_page_flags(struct page *page)
u |= 1 << KPF_COMPOUND_TAIL;
if (PageHuge(page))
u |= 1 << KPF_HUGE;
- else if (PageTransCompound(page))
+ /*
+ * PageTransCompound can be true for non-huge compound pages (slab
+ * pages or pages allocated by drivers with __GFP_COMP) because it
+ * just checks PG_head/PG_tail, so we need to check PageLRU to make
+ * sure a given page is a thp, not a non-huge compound page.
+ */
+ else if (PageTransCompound(page) && PageLRU(compound_trans_head(page)))
u |= 1 << KPF_THP;

/*
--
1.7.11.4


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