[RFC 2/2] page-flags: Catch the double setter of page flags

From: Chintan Pandya
Date: Mon Feb 11 2019 - 07:54:06 EST

Some of the page flags, like PG_locked is not supposed to
be set twice. Currently, there is no protection around this
and many callers directly tries to set this bit. Others
follow trylock_page() which is much safer version of the
same. But, for performance issues, we may not want to
implement wait-until-set. So, at least, find out who is
doing double setting and fix them.

Change-Id: I1295fcb8527ce4b54d5d11c11287fc7516006cf0
Signed-off-by: Chintan Pandya <chintan.pandya@xxxxxxxxxxx>
include/linux/page-flags.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index a56a9bd4bc6b..e307775c2b4a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -208,7 +208,7 @@ static __always_inline int Page##uname(struct page *page) \

#define SETPAGEFLAG(uname, lname, policy) \
static __always_inline void SetPage##uname(struct page *page) \
- { set_bit(PG_##lname, &policy(page, 1)->flags); }
+ { WARN_ON(test_and_set_bit(PG_##lname, &policy(page, 1)->flags)); }

#define CLEARPAGEFLAG(uname, lname, policy) \
static __always_inline void ClearPage##uname(struct page *page) \