On Mon, Sep 10, 2018 at 03:09:29AM -0700, tip-bot for Peter Zijlstra wrote:
> Commit-ID: cb538267ea1e9e025ec692577c9ae75797261889
> Gitweb: https://git.kernel.org/tip/cb538267ea1e9e025ec692577c9ae75797261889
> Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> AuthorDate: Tue, 31 Jul 2018 14:35:32 +0200
> Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> CommitDate: Mon, 10 Sep 2018 10:16:38 +0200
>
> jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations
>
> Weirdly we seem to have forgotten this...
This of course instantly triggered a false positive :/
---
Subject: 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.
Fixes: cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations")
Reported-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
kernel/cpu.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 0097acec1c71..08c168b159da 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -616,6 +616,12 @@ 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.
+ */
+ rwsem_acquire(&cpu_hotplug_lock.rw_sem.dep_map, 0, 0, _THIS_IP_);
cpuhp_lock_acquire(bringup);
if (st->single) {
@@ -661,6 +667,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
}
cpuhp_lock_release(bringup);
+ rwsem_release(&cpu_hotplug_lock.rw_sem.dep_map, 1, _THIS_IP_);
if (!st->should_run)
complete_ap_thread(st, bringup);
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