Patchwork [02/10] arm: Use clear_tasks_mm_cpumask()

mail settings
Submitter Anton Vorontsov
Date March 24, 2012, 10:28 a.m.
Message ID <20120324102808.GB29067@lizard>
Download mbox | patch
Permalink /patch/148500/
State Not Applicable
Headers show


Anton Vorontsov - March 24, 2012, 10:28 a.m.
Current CPU hotplug code has some task->mm handling issues:

1. Working with task->mm w/o getting mm or grabing the task lock is
   dangerous as ->mm might disappear (exit_mm() assigns NULL under
   task_lock(), so tasklist lock is not enough).

   We can't use get_task_mm()/mmput() pair as mmput() might sleep,
   so we must take the task lock while handle its mm.

2. Checking for process->mm is not enough because process' main
   thread may exit or detach its mm via use_mm(), but other threads
   may still have a valid mm.

   To fix this we would need to use find_lock_task_mm(), which would
   walk up all threads and returns an appropriate task (with task
   lock held).

clear_tasks_mm_cpumask() has all the issues fixed, so let's use it.

Suggested-by: Oleg Nesterov <>
Signed-off-by: Anton Vorontsov <>
 arch/arm/kernel/smp.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)


diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index cdeb727..880b93a 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -136,7 +136,6 @@  static void percpu_timer_stop(void);
 int __cpu_disable(void)
 	unsigned int cpu = smp_processor_id();
-	struct task_struct *p;
 	int ret;
 	ret = platform_cpu_disable(cpu);
@@ -166,12 +165,7 @@  int __cpu_disable(void)
-	read_lock(&tasklist_lock);
-	for_each_process(p) {
-		if (p->mm)
-			cpumask_clear_cpu(cpu, mm_cpumask(p->mm));
-	}
-	read_unlock(&tasklist_lock);
+	clear_tasks_mm_cpumask(cpu);
 	return 0;