[tip:locking/core] locking/lockdep, cpu/hotplug: Annotate AP thread

[tip-bot for Peter Zijlstra]

Commit-ID:  cb92173d1f0474784c6171a9d3fdbbca0ee53554
Gitweb:     https://git.kernel.org/tip/cb92173d1f0474784c6171a9d3fdbbca0ee53554
Author:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Tue, 11 Sep 2018 11:51:27 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 11 Sep 2018 20:01:03 +0200

locking/lockdep, cpu/hotplug: Annotate AP thread

Anybody trying to assert the cpu_hotplug_lock is held (lockdep_assert_cpus_held())
from AP callbacks will fail, because the lock is held by the BP.

Stick in an explicit annotation in cpuhp_thread_fun() to make this work.

Reported-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-tip-commits@xxxxxxxxxxxxxxx
Fixes: cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations")
Link: http://lkml.kernel.org/r/20180911095127.GT24082@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/cpu.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 0097acec1c71..be4859f07153 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -315,6 +315,16 @@ void lockdep_assert_cpus_held(void)
 	percpu_rwsem_assert_held(&cpu_hotplug_lock);
 }
 
+static void lockdep_acquire_cpus_lock(void)
+{
+	rwsem_acquire(&cpu_hotplug_lock.rw_sem.dep_map, 0, 0, _THIS_IP_);
+}
+
+static void lockdep_release_cpus_lock(void)
+{
+	rwsem_release(&cpu_hotplug_lock.rw_sem.dep_map, 1, _THIS_IP_);
+}
+
 /*
  * Wait for currently running CPU hotplug operations to complete (if any) and
  * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
@@ -344,6 +354,17 @@ void cpu_hotplug_enable(void)
 	cpu_maps_update_done();
 }
 EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
+
+#else
+
+static void lockdep_acquire_cpus_lock(void)
+{
+}
+
+static void lockdep_release_cpus_lock(void)
+{
+}
+
 #endif	/* CONFIG_HOTPLUG_CPU */
 
 #ifdef CONFIG_HOTPLUG_SMT
@@ -616,6 +637,12 @@ static void cpuhp_thread_fun(unsigned int cpu)
 	 */
 	smp_mb();
 
+	/*
+	 * The BP holds the hotplug lock, but we're now running on the AP,
+	 * ensure that anybody asserting the lock is held, will actually find
+	 * it so.
+	 */
+	lockdep_acquire_cpus_lock();
 	cpuhp_lock_acquire(bringup);
 
 	if (st->single) {
@@ -661,6 +688,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
 	}
 
 	cpuhp_lock_release(bringup);
+	lockdep_release_cpus_lock();
 
 	if (!st->should_run)
 		complete_ap_thread(st, bringup);