1 files changed, 20 insertions, 1 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 356450f09c1f..5d220234b3ca 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -64,6 +64,8 @@ static struct {
          * an ongoing cpu hotplug operation.
          */
         int refcount;
+        /* And allows lockless put_online_cpus(). */
+        atomic_t puts_pending;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
         struct lockdep_map dep_map;
@@ -84,6 +86,16 @@ static struct {
 #define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
 #define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
 
+static void apply_puts_pending(int max)
+{
+        int delta;
+
+        if (atomic_read(&cpu_hotplug.puts_pending) >= max) {
+                delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
+                cpu_hotplug.refcount -= delta;
+        }
+}
+
 void get_online_cpus(void)
 {
         might_sleep();
@@ -91,6 +103,7 @@ void get_online_cpus(void)
                 return;
         cpuhp_lock_acquire_read();
         mutex_lock(&cpu_hotplug.lock);
+        apply_puts_pending(65536);
         cpu_hotplug.refcount++;
         mutex_unlock(&cpu_hotplug.lock);
 }
@@ -103,6 +116,7 @@ bool try_get_online_cpus(void)
         if (!mutex_trylock(&cpu_hotplug.lock))
                 return false;
         cpuhp_lock_acquire_tryread();
+        apply_puts_pending(65536);
         cpu_hotplug.refcount++;
         mutex_unlock(&cpu_hotplug.lock);
         return true;
@@ -113,7 +127,11 @@ void put_online_cpus(void)
 {
         if (cpu_hotplug.active_writer == current)
                 return;
-        mutex_lock(&cpu_hotplug.lock);
+        if (!mutex_trylock(&cpu_hotplug.lock)) {
+                atomic_inc(&cpu_hotplug.puts_pending);
+                cpuhp_lock_release();
+                return;
+        }
 
         if (WARN_ON(!cpu_hotplug.refcount))
                 cpu_hotplug.refcount++; /* try to fix things up */
@@ -155,6 +173,7 @@ void cpu_hotplug_begin(void)
         cpuhp_lock_acquire();
         for (;;) {
                 mutex_lock(&cpu_hotplug.lock);
+                apply_puts_pending(1);
                 if (likely(!cpu_hotplug.refcount))
                         break;
                 __set_current_state(TASK_UNINTERRUPTIBLE);