[tip:sched/urgent] sched/core: WARN() when migrating to an offline CPU

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  4ff9083b8a9a80bdf4ebbbec22cda4cbfb60f7aa
Gitweb:     http://git.kernel.org/tip/4ff9083b8a9a80bdf4ebbbec22cda4cbfb60f7aa
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 7 Sep 2017 17:03:52 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 12 Sep 2017 17:41:04 +0200

sched/core: WARN() when migrating to an offline CPU

Migrating tasks to offline CPUs is a pretty big fail, warn about it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170907150614.094206976@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 136a76d..18a6966 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1173,6 +1173,10 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 	WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
 				      lockdep_is_held(&task_rq(p)->lock)));
 #endif
+	/*
+	 * Clearly, migrating tasks to offline CPUs is a fairly daft thing.
+	 */
+	WARN_ON_ONCE(!cpu_online(new_cpu));
 #endif
 
 	trace_sched_migrate_task(p, new_cpu);