Revert "cpuset: Make cpuset hotplug synchronous"

This reverts commit a49e4629b5ed ("cpuset: Make cpuset hotplug synchronous") as
it may deadlock with cpu hotplug path.

Link: http://lkml.kernel.org/r/F0388D99-84D7-453B-9B6B-EEFF0E7BE4CC@lca.pw
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Qian Cai <cai@lca.pw>
Cc: Prateek Sood <prsood@codeaurora.org>

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index cede4cb..04c20de 100644 (file)
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -54,6 +54,7 @@ extern int cpuset_init(void);
 extern void cpuset_init_smp(void);
 extern void cpuset_force_rebuild(void);
 extern void cpuset_update_active_cpus(void);
+extern void cpuset_wait_for_hotplug(void);
 extern void cpuset_read_lock(void);
 extern void cpuset_read_unlock(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
@@ -175,6 +176,8 @@ static inline void cpuset_update_active_cpus(void)
        partition_sched_domains(1, NULL, NULL);
 }
 
+static inline void cpuset_wait_for_hotplug(void) { }
+
 static inline void cpuset_read_lock(void) { }
 static inline void cpuset_read_unlock(void) { }
 

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index cafd4d2..58f5073 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3101,7 +3101,7 @@ update_tasks:
 }
 
 /**
- * cpuset_hotplug - handle CPU/memory hotunplug for a cpuset
+ * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
  *
  * This function is called after either CPU or memory configuration has
  * changed and updates cpuset accordingly.  The top_cpuset is always
@@ -3116,7 +3116,7 @@ update_tasks:
  * Note that CPU offlining during suspend is ignored.  We don't modify
  * cpusets across suspend/resume cycles at all.
  */
-static void cpuset_hotplug(bool use_cpu_hp_lock)
+static void cpuset_hotplug_workfn(struct work_struct *work)
 {
        static cpumask_t new_cpus;
        static nodemask_t new_mems;
@@ -3201,32 +3201,25 @@ static void cpuset_hotplug(bool use_cpu_hp_lock)
        /* rebuild sched domains if cpus_allowed has changed */
        if (cpus_updated || force_rebuild) {
                force_rebuild = false;
-               if (use_cpu_hp_lock)
-                       rebuild_sched_domains();
-               else {
-                       /* Acquiring cpu_hotplug_lock is not required.
-                        * When cpuset_hotplug() is called in hotplug path,
-                        * cpu_hotplug_lock is held by the hotplug context
-                        * which is waiting for cpuhp_thread_fun to indicate
-                        * completion of callback.
-                       */
-                       percpu_down_write(&cpuset_rwsem);
-                       rebuild_sched_domains_locked();
-                       percpu_up_write(&cpuset_rwsem);
-               }
+               rebuild_sched_domains();
        }
 
        free_cpumasks(NULL, ptmp);
 }
 
-static void cpuset_hotplug_workfn(struct work_struct *work)
+void cpuset_update_active_cpus(void)
 {
-       cpuset_hotplug(true);
+       /*
+        * We're inside cpu hotplug critical region which usually nests
+        * inside cgroup synchronization.  Bounce actual hotplug processing
+        * to a work item to avoid reverse locking order.
+        */
+       schedule_work(&cpuset_hotplug_work);
 }
 
-void cpuset_update_active_cpus(void)
+void cpuset_wait_for_hotplug(void)
 {
-       cpuset_hotplug(false);
+       flush_work(&cpuset_hotplug_work);
 }
 
 /*

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 08f7019..4b6a54d 100644 (file)
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -204,6 +204,8 @@ void thaw_processes(void)
        __usermodehelper_set_disable_depth(UMH_FREEZING);
        thaw_workqueues();
 
+       cpuset_wait_for_hotplug();
+
        read_lock(&tasklist_lock);
        for_each_process_thread(g, p) {
                /* No other threads should have PF_SUSPEND_TASK set */