From: Satoru Takeuchi 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 Cc: Rusty Russell Cc: Ingo Molnar Cc: Oleg Nesterov Cc: Ashok Raj Cc: Gautham R Shenoy Signed-off-by: Andrew Morton --- 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, ¶m); 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, ¶m); kthread_bind(p, cpu); wake_up_process(p); wait_for_completion(&smdata.done); _