linux-kernel - [PATCH] mm/vmscan: fix unsequenced modification and access warning

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Date:   Tue,  9 May 2017 23:53:28 -0700
From:   Nick Desaulniers <nick.desaulniers@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        mgorman@...hsingularity.net, mhocko@...e.com, vbabka@...e.cz,
        minchan@...nel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <nick.desaulniers@...il.com>
Subject: [PATCH] mm/vmscan: fix unsequenced modification and access warning

Clang flags this file with the -Wunsequenced error that GCC does not
have.

unsequenced modification and access to 'gfp_mask'

It seems that gfp_mask is both read and written without a sequence point
in between, which is undefined behavior.

Signed-off-by: Nick Desaulniers <nick.desaulniers@...il.com>
---
 mm/vmscan.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4e7ed65842af..74785908822c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2958,7 +2958,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 	unsigned long nr_reclaimed;
 	struct scan_control sc = {
 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
-		.gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)),
+		.gfp_mask = current_gfp_context(gfp_mask),
 		.reclaim_idx = gfp_zone(gfp_mask),
 		.order = order,
 		.nodemask = nodemask,
@@ -2968,6 +2968,8 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 		.may_swap = 1,
 	};
 
+	gfp_mask = sc.gfp_mask;
+
 	/*
 	 * Do not enter reclaim if fatal signal was delivered while throttled.
 	 * 1 is returned so that the page allocator does not OOM kill at this
-- 
2.11.0