Re: [PATCH 1/2] Fix stop_machine_run problem with naughty real time process

[Satoru Takeuchi]

At Fri, 11 May 2007 17:49:20 +0900,
Satoru Takeuchi wrote:
> 
> Hi,
> 
> I wrote patches which fixes the problem regarding stop_machine_run() and
> cpu hotplug.

Sorry, there were extra tabs. Fixed.

Thanks,

Satoru

---
Fix stop_machine_run() problem with naughty real time process

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 <[EMAIL PROTECTED]>

Index: linux-2.6.21/kernel/stop_machine.c
===================================================================
--- linux-2.6.21.orig/kernel/stop_machine.c     2007-05-11 13:45:34.000000000 
+0900
+++ linux-2.6.21/kernel/stop_machine.c  2007-05-11 14:49:17.000000000 +0900
@@ -89,10 +89,6 @@ 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;
@@ -184,6 +180,10 @@ 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);
-
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