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

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Date:   Mon, 11 Feb 2019 12:53:55 +0000
From:   Chintan Pandya <chintan.pandya@...plus.com>
To:     Linux Upstream <linux.upstream@...plus.com>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "jack@...e.cz" <jack@...e.cz>,
        "mawilcox@...rosoft.com" <mawilcox@...rosoft.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Chintan Pandya <chintan.pandya@...plus.com>
Subject: [RFC 2/2] page-flags: Catch the double setter of page flags

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@...plus.com>
---
 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)		\
-- 
2.17.1