The WARN_ON_ONCE() in ct_kernel_exit_state() follows the call to
ct_state_inc(), which means that RCU is not watching this WARN_ON_ONCE().
This can (and does) result in extraneous lockdep warnings when this
WARN_ON_ONCE() triggers. These extraneous warnings are the opposite
of helpful.
Therefore, invert the WARN_ON_ONCE() condition and move it before the
call to ct_state_inc(). This does mean that the ct_state_inc() return
value can no longer be used in the WARN_ON_ONCE() condition, so discard
this return value and instead use a call to rcu_is_watching_curr_cpu().
This call is executed only in CONFIG_RCU_EQS_DEBUG=y kernels, so there
is no added overhead in production use.
Reported-by: Breno Leitao <leitao@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reviewed-by: Valentin Schneider <vschneid@xxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 938c48952d26..fb5be6e9b423 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -80,17 +80,16 @@ static __always_inline void rcu_task_trace_heavyweight_exit(void)
*/
static noinstr void ct_kernel_exit_state(int offset)
{
- int seq;
-
/*
* CPUs seeing atomic_add_return() must see prior RCU read-side
* critical sections, and we also must force ordering with the
* next idle sojourn.
*/
rcu_task_trace_heavyweight_enter(); // Before CT state update!
- seq = ct_state_inc(offset);
- // RCU is no longer watching. Better be in extended quiescent state!
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & CT_RCU_WATCHING));
+ // RCU is still watching. Better not be in extended quiescent state!
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !rcu_is_watching_curr_cpu());
+ (void)ct_state_inc(offset);
+ // RCU is no longer watching.
}
/*
