2022-07-12 08:43:31

by Zqiang

Subject: [PATCH 1/2] rcu-tasks: Convert RCU_LOCKDEP_WARN() to WARN_ONCE()

For kernel build with CONFIG_PROVE_RCU=y and CONFIG_DEBUG_LOCK_ALLOC=y,
when the synchronize_rcu_tasks_generic() called occurs during the
rcu_scheduler_active variable is RCU_SCHEDULER_INACTIVE, the warnings
will be trigger, however the warnings is not actually triggered because
the debug_lockdep_rcu_enabled() return false(the rcu_scheduler_active !=
RCU_SCHEDULER_INACTIVE condition is false).

This commit replace RCU_LOCKDEP_WARN() with WARN_ONCE() to trigger
warnings.

Signed-off-by: Zqiang <[email protected]>
---
kernel/rcu/tasks.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 83c7e6620d40..469bf2a3b505 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -560,7 +560,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
{
/* Complain if the scheduler has not started. */
- RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
+ WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
"synchronize_rcu_tasks called too soon");

// If the grace-period kthread is running, use it.
--
2.25.1

2022-07-12 18:01:14

by Paul E. McKenney

Subject: Re: [PATCH 1/2] rcu-tasks: Convert RCU_LOCKDEP_WARN() to WARN_ONCE()

On Tue, Jul 12, 2022 at 04:26:05PM +0800, Zqiang wrote:
> For kernel build with CONFIG_PROVE_RCU=y and CONFIG_DEBUG_LOCK_ALLOC=y,
> when the synchronize_rcu_tasks_generic() called occurs during the
> rcu_scheduler_active variable is RCU_SCHEDULER_INACTIVE, the warnings
> will be trigger, however the warnings is not actually triggered because
> the debug_lockdep_rcu_enabled() return false(the rcu_scheduler_active !=
> RCU_SCHEDULER_INACTIVE condition is false).
>
> This commit replace RCU_LOCKDEP_WARN() with WARN_ONCE() to trigger
> warnings.
>
> Signed-off-by: Zqiang <[email protected]>

Good catch, thank you!

Queued with wordsmithing as follows. As always, please check to see
if I wordsmithed something out of existence.

Thanx, Paul

------------------------------------------------------------------------

commit 4dbfea53caf3e226e3273fc5947e9041e2ad34ab
Author: Zqiang <[email protected]>
Date: Tue Jul 12 16:26:05 2022 +0800

rcu-tasks: Convert RCU_LOCKDEP_WARN() to WARN_ONCE()

Kernels built with CONFIG_PROVE_RCU=y and CONFIG_DEBUG_LOCK_ALLOC=y
attempt to emit a warning when the synchronize_rcu_tasks_generic()
function is called during early boot while the rcu_scheduler_active
variable is RCU_SCHEDULER_INACTIVE. However the warnings is not
actually be printed because the debug_lockdep_rcu_enabled() returns
false, exactly because the rcu_scheduler_active variable is still equal
to RCU_SCHEDULER_INACTIVE.

This commit therefore replaces RCU_LOCKDEP_WARN() with WARN_ONCE()
to force these warnings to actually be printed.

Signed-off-by: Zqiang <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 83c7e6620d403..469bf2a3b505e 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -560,7 +560,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
{
/* Complain if the scheduler has not started. */
- RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
+ WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
"synchronize_rcu_tasks called too soon");

// If the grace-period kthread is running, use it.