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@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>
Cc: linux-tip-commits@vger.kernel.org
Fixes: cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations")
Link: http://lkml.kernel.org/r/20180911095127.GT24082@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 0097acec1c717dee6948e50b57ab4c4bb0c15ac7..be4859f0715313000b18e81c208029c1e4e0b93b 100644 (file)
--- 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);