linux-kernel - Re: [PATCH V2] lockdep: suggest the fix for "lockdep bfs error:-1" on print_bfs

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Message-ID: <20240802151042.GM39708@noisy.programming.kicks-ass.net>
Date: Fri, 2 Aug 2024 17:10:42 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] lockdep: suggest the fix for "lockdep bfs error:-1"
 on print_bfs_bug

On Tue, Jul 30, 2024 at 02:45:47PM -0300, Luis Claudio R. Goncalves wrote:
> When lockdep fails while performing the Breadth-first-search operation
> due to lack of memory, hint that increasing the value of the config
> switch LOCKDEP_CIRCULAR_QUEUE_BITS should fix the warning.
> 
> Preface the scary backtrace with the suggestion:
> 
>     [  163.849242] Increase LOCKDEP_CIRCULAR_QUEUE_BITS to avoid this warning:
>     [  163.849248] ------------[ cut here ]------------
>     [  163.849250] lockdep bfs error:-1
>     [  163.849263] WARNING: CPU: 24 PID: 2454 at kernel/locking/lockdep.c:2091 print_bfs_bug+0x27/0x40
>     ...
> 
> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
> Reviewed-by: Waiman Long <longman@...hat.com>
> Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@...hat.com>

Thanks!

> ---
> 
> Changes in v2:
>   - removed extra space from the if condition.
> 
>  kernel/locking/lockdep.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 58c88220a478a..1cf6d9fdddc9c 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -2067,6 +2067,9 @@ static noinline void print_bfs_bug(int ret)
>  	/*
>  	 * Breadth-first-search failed, graph got corrupted?
>  	 */
> +	if (ret == BFS_EQUEUEFULL)
> +		pr_warn("Increase LOCKDEP_CIRCULAR_QUEUE_BITS to avoid this warning:\n");
> +
>  	WARN(1, "lockdep bfs error:%d\n", ret);
>  }
>  
> -- 
> 2.45.2
>