linux-kernel - Re: [PATCH 1/2] rcu-tasks: Convert RCU_LOCKDEP_WARN() to WARN

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Message-ID: <20220712172842.GW1790663@paulmck-ThinkPad-P17-Gen-1>
Date:   Tue, 12 Jul 2022 10:28:42 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
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 <qiang1.zhang@...el.com>

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 <qiang1.zhang@...el.com>
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 <qiang1.zhang@...el.com>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

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.