[PATCH] cpuset: use rcu_read_lock() to protect task_cs()

[Li Zefan]

We no longer use task_lock() to protect tsk->cgroups.

Reported-by: Fengguang Wu <fengguang...@intel.com>
Signed-off-by: Li Zefan <lize...@huawei.com>
---
 kernel/cpuset.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index c63a0d9..4b3560d 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2235,10 +2235,10 @@ void cpuset_cpus_allowed(struct task_struct *tsk, 
struct cpumask *pmask)
        struct cpuset *cpus_cs;
 
        mutex_lock(&callback_mutex);
-       task_lock(tsk);
+       rcu_read_lock();
        cpus_cs = effective_cpumask_cpuset(task_cs(tsk));
        guarantee_online_cpus(cpus_cs, pmask);
-       task_unlock(tsk);
+       rcu_read_unlock();
        mutex_unlock(&callback_mutex);
 }
 
@@ -2291,10 +2291,10 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
        nodemask_t mask;
 
        mutex_lock(&callback_mutex);
-       task_lock(tsk);
+       rcu_read_lock();
        mems_cs = effective_nodemask_cpuset(task_cs(tsk));
        guarantee_online_mems(mems_cs, &mask);
-       task_unlock(tsk);
+       rcu_read_unlock();
        mutex_unlock(&callback_mutex);
 
        return mask;
@@ -2410,10 +2410,10 @@ int __cpuset_node_allowed_softwall(int node, gfp_t 
gfp_mask)
        /* Not hardwall and node outside mems_allowed: scan up cpusets */
        mutex_lock(&callback_mutex);
 
-       task_lock(current);
+       rcu_read_lock();
        cs = nearest_hardwall_ancestor(task_cs(current));
        allowed = node_isset(node, cs->mems_allowed);
-       task_unlock(current);
+       rcu_read_unlock();
 
        mutex_unlock(&callback_mutex);
        return allowed;
@@ -2539,24 +2539,26 @@ int cpuset_mems_allowed_intersects(const struct 
task_struct *tsk1,
  * @task: pointer to task_struct of some task.
  *
  * Description: Prints @task's name, cpuset name, and cached copy of its
- * mems_allowed to the kernel log.  Must hold task_lock(task) to allow
- * dereferencing task_cs(task).
+ * mems_allowed to the kernel log.
  */
 void cpuset_print_task_mems_allowed(struct task_struct *tsk)
 {
         /* Statically allocated to prevent using excess stack. */
        static char cpuset_nodelist[CPUSET_NODELIST_LEN];
        static DEFINE_SPINLOCK(cpuset_buffer_lock);
-       struct cgroup *cgrp = task_cs(tsk)->css.cgroup;
+       struct cgroup *cgrp;
 
        spin_lock(&cpuset_buffer_lock);
+       rcu_read_lock();
 
+       cgrp = task_cs(tsk)->css.cgroup;
        nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
                           tsk->mems_allowed);
        printk(KERN_INFO "%s cpuset=", tsk->comm);
        pr_cont_cgroup_name(cgrp);
        pr_cont(" mems_allowed=%s\n", cpuset_nodelist);
 
+       rcu_read_unlock();
        spin_unlock(&cpuset_buffer_lock);
 }
 
@@ -2588,9 +2590,9 @@ int cpuset_memory_pressure_enabled __read_mostly;
 
 void __cpuset_memory_pressure_bump(void)
 {
-       task_lock(current);
+       rcu_read_lock();
        fmeter_markevent(&task_cs(current)->fmeter);
-       task_unlock(current);
+       rcu_read_unlock();
 }
 
 #ifdef CONFIG_PROC_PID_CPUSET
-- 
1.8.0.2
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