[patch 119/262] mm: page_alloc: use migrate_disable() in drain_local_pages_wq()

Andrew Morton
2021-11-05T20:40:55Z

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: mm: page_alloc: use migrate_disable() in drain_local_pages_wq()

drain_local_pages_wq() disables preemption to avoid CPU migration during
CPU hotplug and can't use cpus_read_lock().

Using migrate_disable() works here, too. The scheduler won't take the CPU
offline until the task left the migrate-disable section. The problem with
disabled preemption here is that drain_local_pages() acquires locks which
are turned into sleeping locks on PREEMPT_RT and can't be acquired with
disabled preemption.

Use migrate_disable() in drain_local_pages_wq().

Link: https://lkml.kernel.org/r/20211015210933.viw6rjvo64qtqxn4@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/page_alloc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-use-migrate_disable-in-drain_local_pages_wq
+++ a/mm/page_alloc.c
@@ -3141,9 +3141,9 @@ static void drain_local_pages_wq(struct
* cpu which is alright but we also have to make sure to not move to
* a different one.
*/
- preempt_disable();
+ migrate_disable();
drain_local_pages(drain->zone);
- preempt_enable();
+ migrate_enable();
}

/*
_