commit ce48c146495a1a50e48cdbfbfaba3e708be7c07c
author Peter Zijlstra <peterz@infradead.org> Mon Jan 22 22:53:28 2018 +0100
committer Ingo Molnar <mingo@kernel.org> Wed Jan 24 10:03:44 2018 +0100
tree 6aabd7d32c16454175afdb2a20352056d9beb71a
parent 1f07476ec143bbed7bf0b641749783b1094b4c4f

sched/core: Fix cpu.max vs. cpuhotplug deadlock

Tejun reported the following cpu-hotplug lock (percpu-rwsem) read recursion:

  tg_set_cfs_bandwidth()
    get_online_cpus()
      cpus_read_lock()

    cfs_bandwidth_usage_inc()
      static_key_slow_inc()
        cpus_read_lock()

Reported-by: Tejun Heo <tj@kernel.org>
Tested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180122215328.GP3397@worktop
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/jump_label.c

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 8594d24..b451709 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -79,7 +79,7 @@ int static_key_count(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_count);
 
-static void static_key_slow_inc_cpuslocked(struct static_key *key)
+void static_key_slow_inc_cpuslocked(struct static_key *key)
 {
 	int v, v1;
 
@@ -180,7 +180,7 @@ void static_key_disable(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_disable);
 
-static void static_key_slow_dec_cpuslocked(struct static_key *key,
+static void __static_key_slow_dec_cpuslocked(struct static_key *key,
 					   unsigned long rate_limit,
 					   struct delayed_work *work)
 {
@@ -211,7 +211,7 @@ static void __static_key_slow_dec(struct static_key *key,
 				  struct delayed_work *work)
 {
 	cpus_read_lock();
-	static_key_slow_dec_cpuslocked(key, rate_limit, work);
+	__static_key_slow_dec_cpuslocked(key, rate_limit, work);
 	cpus_read_unlock();
 }
 
@@ -229,6 +229,12 @@ void static_key_slow_dec(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_slow_dec);
 
+void static_key_slow_dec_cpuslocked(struct static_key *key)
+{
+	STATIC_KEY_CHECK_USE(key);
+	__static_key_slow_dec_cpuslocked(key, 0, NULL);
+}
+
 void static_key_slow_dec_deferred(struct static_key_deferred *key)
 {
 	STATIC_KEY_CHECK_USE(key);