+ fix-stop_machine_run-problem-with-naughty-real-time-process.patch added to -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     Fix stop_machine_run problem with naughty real time process
has been added to the -mm tree.  Its filename is
     fix-stop_machine_run-problem-with-naughty-real-time-process.patch

*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this

------------------------------------------------------
Subject: Fix stop_machine_run problem with naughty real time process
From: Satoru Takeuchi <takeuchi_satoru@xxxxxxxxxxxxxx>

stop_machine_run() does its work on "kstopmachine" thread having max
priority.  However that thread get such priority after woken up. 
Therefore, in the following case ...

  - "kstopmachine" try to run on CPU1

  - There is a real time process which doesn't relinquish CPU time
    voluntary on CPU1

...  "kstopmachine" can't start to run and the CPU on which
    stop_machine_run() is runing hangs up.  To fix this problem, call
    sched_setscheduler() before waking up that thread.

Signed-off-by: Satoru Takeuchi <takeuchi_satoru@xxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: Gautham R Shenoy <ego@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/stop_machine.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff -puN kernel/stop_machine.c~fix-stop_machine_run-problem-with-naughty-real-time-process kernel/stop_machine.c
--- a/kernel/stop_machine.c~fix-stop_machine_run-problem-with-naughty-real-time-process
+++ a/kernel/stop_machine.c
@@ -93,10 +93,6 @@ static void stopmachine_set_state(enum s
 static int stop_machine(void)
 {
 	int i, ret = 0;
-	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
-
-	/* One high-prio thread per cpu.  We'll do this one. */
-	sched_setscheduler(current, SCHED_FIFO, &param);
 
 	atomic_set(&stopmachine_thread_ack, 0);
 	stopmachine_num_threads = 0;
@@ -189,6 +185,10 @@ struct task_struct *__stop_machine_run(i
 
 	p = kthread_create(do_stop, &smdata, "kstopmachine");
 	if (!IS_ERR(p)) {
+		struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
+
+		/* One high-prio thread per cpu.  We'll do this one. */
+		sched_setscheduler(p, SCHED_FIFO, &param);
 		kthread_bind(p, cpu);
 		wake_up_process(p);
 		wait_for_completion(&smdata.done);
_

Patches currently in -mm which might be from takeuchi_satoru@xxxxxxxxxxxxxx are

fix-stop_machine_run-problem-with-naughty-real-time-process.patch
cpu-hotplug-fix-ksoftirqd-termination-on-cpu-hotplug-with-naughty-realtime-process.patch

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