On Mon, Feb 01, 2021 at 10:50:58AM +0100, Peter Zijlstra wrote:

quoted

quoted

  queued_spin_unlock arch/x86/include/asm/qspinlock.h:56 [inline]
  lockdep_unlock+0x10e/0x290 kernel/locking/lockdep.c:124
  debug_locks_off_graph_unlock kernel/locking/lockdep.c:165 [inline]
  print_usage_bug kernel/locking/lockdep.c:3710 [inline]

Ha, I think you hit a bug in lockdep.

Something like so I suppose.

---
Subject: locking/lockdep: Avoid unmatched unlock
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon Feb 1 11:55:38 CET 2021

Commit f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI"
inversions") overlooked that print_usage_bug() releases the graph_lock
and called it without the graph lock held.

Fixes: f6f48e180404 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
  kernel/locking/lockdep.c |    3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c

@@ -3773,7 +3773,7 @@ static void
  print_usage_bug(struct task_struct *curr, struct held_lock *this,
  		enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
  {
-	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
+	if (!debug_locks_off() || debug_locks_silent)
  		return;
  
  	pr_warn("\n");

@@ -3814,6 +3814,7 @@ valid_state(struct task_struct *curr, st
  	    enum lock_usage_bit new_bit, enum lock_usage_bit bad_bit)
  {
  	if (unlikely(hlock_class(this)->usage_mask & (1 << bad_bit))) {
+		graph_unlock()
  		print_usage_bug(curr, this, bad_bit, new_bit);
  		return 0;
  	}