[PATCH 3/8] arm: Fix possible race on task->mm

From: Anton Vorontsov
Date: Tue Feb 07 2012 - 01:50:11 EST

Checking for task->mm 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 let's take the task lock while we care about its mm.

Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
arch/arm/kernel/smp.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 57db122..85db3f2 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -168,8 +168,10 @@ int __cpu_disable(void)

for_each_process(p) {
+ task_lock(p);
if (p->mm)
cpumask_clear_cpu(cpu, mm_cpumask(p->mm));
+ task_unlock(p);


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