[PATCH 3/9] powerpc: Use clear_tasks_mm_cpumask()

From: Anton Vorontsov
Date: Mon Apr 23 2012 - 03:09:53 EST

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 <oleg@xxxxxxxxxx>
Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
arch/powerpc/mm/mmu_context_nohash.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/mm/mmu_context_nohash.c b/arch/powerpc/mm/mmu_context_nohash.c
index 5b63bd3..e779642 100644
--- a/arch/powerpc/mm/mmu_context_nohash.c
+++ b/arch/powerpc/mm/mmu_context_nohash.c
@@ -333,9 +333,7 @@ static int __cpuinit mmu_context_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
unsigned int cpu = (unsigned int)(long)hcpu;
- struct task_struct *p;
/* We don't touch CPU 0 map, it's allocated at aboot and kept
* around forever
@@ -358,12 +356,7 @@ static int __cpuinit mmu_context_cpu_notify(struct notifier_block *self,
stale_map[cpu] = NULL;

/* We also clear the cpu_vm_mask bits of CPUs going away */
- 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);

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