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Date:   Sun, 18 Sep 2022 11:31:46 -0700
From:   Boqun Feng <boqun.feng@gmail.com>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] lockdep: report name and key when look_up_lock_class()
 got confused
Message-ID: <YydkEtcVc0GtCizz@boqun-archlinux>
References: <55111c45-0f8f-c6f9-640c-6919939b77dd@I-love.SAKURA.ne.jp>
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On Mon, Sep 19, 2022 at 12:01:30AM +0900, Tetsuo Handa wrote:
> Printing this information will be helpful.
> 
>   ------------[ cut here ]------------
>   class->name=slock-AF_INET6 lock->name=l2tp_sock lock->key=l2tp_socket_class
>   WARNING: CPU: 2 PID: 9237 at kernel/locking/lockdep.c:940 look_up_lock_class+0xcc/0x140
>   Modules linked in:
>   CPU: 2 PID: 9237 Comm: a.out Not tainted 6.0.0-rc5-00094-ga335366bad13-dirty #860
>   Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>   RIP: 0010:look_up_lock_class+0xcc/0x140
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
>  kernel/locking/lockdep.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 64a13eb56078..a22469dbeeee 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -934,8 +934,10 @@ look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
>  			 * Huh! same key, different name? Did someone trample
>  			 * on some memory? We're most confused.
>  			 */
> -			WARN_ON_ONCE(class->name != lock->name &&
> -				     lock->key != &__lockdep_no_validate__);
> +			WARN_ONCE(class->name != lock->name &&
> +				  lock->key != &__lockdep_no_validate__,
> +				  "class->name=%s lock->name=%s lock->key=%ps\n",
> +				  class->name, lock->name, lock->key);

Maybe more human readable information like:

	  "Looking for class \"%s\" with key %ps, but found a different class \"%s\" with the same key\n"
	  lock->name, lock->key, class->name);

?

Regards,
Boqun

>  			return class;
>  		}
>  	}
> -- 
> 2.34.1
>