From b26bc8cf3d08daa01a12d9e4e6d4dd17554d1b8b Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 12 Dec 2019 10:53:59 +0100
Subject: [PATCH 488/518] sched: migrate_enable: Busy loop until the migration
 request is completed

[ Upstream commit 140d7f54a5fff02898d2ca9802b39548bf7455f1 ]

If user task changes the CPU affinity mask of a running task it will
dispatch migration request if the current CPU is no longer allowed. This
might happen shortly before a task enters a migrate_disable() section.
Upon leaving the migrate_disable() section, the task will notice that
the current CPU is no longer allowed and will will dispatch its own
migration request to move it off the current CPU.
While invoking __schedule() the first migration request will be
processed and the task returns on the "new" CPU with "arg.done = 0". Its
own migration request will be processed shortly after and will result in
memory corruption if the stack memory, designed for request, was used
otherwise in the meantime.

Spin until the migration request has been processed if it was accepted.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
---
 kernel/sched/core.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 00b8b8b20c262..9bfda7818e589 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7004,7 +7004,7 @@ void migrate_enable(void)
 
 	WARN_ON(smp_processor_id() != cpu);
 	if (!is_cpu_allowed(p, cpu)) {
-		struct migration_arg arg = { p };
+		struct migration_arg arg = { .task = p };
 		struct cpu_stop_work work;
 		struct rq_flags rf;
 
@@ -7017,7 +7017,10 @@ void migrate_enable(void)
 				    &arg, &work);
 		tlb_migrate_finish(p->mm);
 		__schedule(true);
-		WARN_ON_ONCE(!arg.done && !work.disabled);
+		if (!work.disabled) {
+			while (!arg.done)
+				cpu_relax();
+		}
 	}
 
 out:
-- 
2.41.0

