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[PATCH AUTOSEL 4.19 28/48] mm: handle lru_add_drain_all for UP properly

From: Michal Hocko <mhocko@xxxxxxxx>

[ Upstream commit 6ea183d60c469560e7b08a83c9804299e84ec9eb ]

Since for_each_cpu(cpu, mask) added by commit 2d3854a37e8b767a
("cpumask: introduce new API, without changing anything") did not
evaluate the mask argument if NR_CPUS == 1 due to CONFIG_SMP=n,
lru_add_drain_all() is hitting WARN_ON() at __flush_work() added by
commit 4d43d395fed12463 ("workqueue: Try to catch flush_work() without
INIT_WORK().") by unconditionally calling flush_work() [1].

Workaround this issue by using CONFIG_SMP=n specific lru_add_drain_all
implementation.  There is no real need to defer the implementation to
the workqueue as the draining is going to happen on the local cpu.  So
alias lru_add_drain_all to lru_add_drain which does all the necessary

[akpm@xxxxxxxxxxxxxxxxxxxx: fix various build warnings]
[1] https://lkml.kernel.org/r/18a30387-6aa5-6123-e67c-57579ecc3f38@xxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20190213124334.GH4525@xxxxxxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Debugged-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
 mm/swap.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 26fc9b5f1b6c..a3fc028e338e 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -321,11 +321,6 @@ static inline void activate_page_drain(int cpu)
-static bool need_activate_page_drain(int cpu)
-	return false;
 void activate_page(struct page *page)
 	struct zone *zone = page_zone(page);
@@ -654,13 +649,15 @@ void lru_add_drain(void)
+#ifdef CONFIG_SMP
+static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
 static void lru_add_drain_per_cpu(struct work_struct *dummy)
-static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
  * Doesn't need any cpu hotplug locking because we do rely on per-cpu
  * kworkers being shut down before our page_alloc_cpu_dead callback is
@@ -703,6 +700,12 @@ void lru_add_drain_all(void)
+void lru_add_drain_all(void)
+	lru_add_drain();
  * release_pages - batched put_page()