From 54bb2b6ed2dce8b51802a0a866f92a9212d411d2 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 5 Nov 2021 13:40:52 -0700
Subject: [PATCH] mm: page_alloc: use migrate_disable() in
 drain_local_pages_wq()

References: bsc#1189998 (PREEMPT_RT prerequisite backports)
Patch-mainline: v5.16-rc1
Git-commit: 9c25cbfcb38462803a3d68f5d88e66a587f5f045

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e611706a3a96..0a9085fa7bb9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3141,9 +3141,9 @@ static void drain_local_pages_wq(struct work_struct *work)
 	 * 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();
 }
 
 /*