cpuset: use rcu_read_lock() to protect task_cs()

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

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 13 insertions, 11 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d8bec21d7a11..8d5324583aa4 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2239,10 +2239,10 @@ 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);
 }
 
@@ -2295,10 +2295,10 @@ 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;
@@ -2414,9 +2414,9 @@ 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));
-        task_unlock(current);
+        rcu_read_unlock();
 
         allowed = node_isset(node, cs->mems_allowed);
         mutex_unlock(&callback_mutex);
@@ -2543,24 +2543,26 @@ 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);
 }
 
@@ -2592,9 +2594,9 @@ 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