Commit 7a71932d authored by Naoya Horiguchi's avatar Naoya Horiguchi Committed by Linus Torvalds

kpageflags: fix wrong KPF_THP on non-huge compound pages

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.
Signed-off-by: default avatarNaoya Horiguchi <>
Acked-by: default avatarKOSAKI Motohiro <>
Acked-by: default avatarDavid Rientjes <>
Reviewed-by: default avatarFengguang Wu <>
Cc: <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent cd8ed2a4
......@@ -115,7 +115,13 @@ u64 stable_page_flags(struct page *page)
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;
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