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[PATCH] lockdep: report name and key when look_up_lock_class() got confused

Tetsuo Handa posted 1 patch 3 years, 6 months ago
There is a newer version of this series
kernel/locking/lockdep.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
[PATCH] lockdep: report name and key when look_up_lock_class() got confused
Posted by Tetsuo Handa 3 years, 6 months ago 
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);
 			return class;
 		}
 	}
-- 
2.34.1
Re: [PATCH] lockdep: report name and key when look_up_lock_class() got confused
Posted by Boqun Feng 3 years, 6 months ago 
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
>
[PATCH v2] lockdep: report name and key when look_up_lock_class() got confused
Posted by Tetsuo Handa 3 years, 6 months ago 
Printing this information will be helpful.

  ------------[ cut here ]------------
  Looking for class "l2tp_sock" with key l2tp_socket_class, but found a different class "slock-AF_INET6" with the same key
  WARNING: CPU: 1 PID: 14195 at kernel/locking/lockdep.c:940 look_up_lock_class+0xcc/0x140
  Modules linked in:
  CPU: 1 PID: 14195 Comm: a.out Not tainted 6.0.0-rc6-dirty #863
  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>
---
Changes in v2:
  Make message more human readable, suggested by Boqun Feng <boqun.feng@gmail.com>.

 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..e3375bc40dad 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__,
+				  "Looking for class \"%s\" with key %ps, but found a different class \"%s\" with the same key\n",
+				  lock->name, lock->key, class->name);
 			return class;
 		}
 	}
-- 
2.34.1
Re: [PATCH v2] lockdep: report name and key when look_up_lock_class() got confused
Posted by Peter Zijlstra 3 years, 6 months ago 
On Mon, Sep 19, 2022 at 09:52:13AM +0900, Tetsuo Handa wrote:
> Printing this information will be helpful.
> 
>   ------------[ cut here ]------------
>   Looking for class "l2tp_sock" with key l2tp_socket_class, but found a different class "slock-AF_INET6" with the same key
>   WARNING: CPU: 1 PID: 14195 at kernel/locking/lockdep.c:940 look_up_lock_class+0xcc/0x140
>   Modules linked in:
>   CPU: 1 PID: 14195 Comm: a.out Not tainted 6.0.0-rc6-dirty #863
>   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>

Urgh, you hitting that WARN enough times to want to improve it seems to
suggest your machine is quite sick.

Anyway, patch is ok I suppose.
Re: [PATCH v2] lockdep: report name and key when look_up_lock_class() got confused
Posted by Tetsuo Handa 3 years, 6 months ago 
On 2022/09/19 19:48, Peter Zijlstra wrote:
> On Mon, Sep 19, 2022 at 09:52:13AM +0900, Tetsuo Handa wrote:
>> Printing this information will be helpful.
>>
>>   ------------[ cut here ]------------
>>   Looking for class "l2tp_sock" with key l2tp_socket_class, but found a different class "slock-AF_INET6" with the same key
>>   WARNING: CPU: 1 PID: 14195 at kernel/locking/lockdep.c:940 look_up_lock_class+0xcc/0x140
>>   Modules linked in:
>>   CPU: 1 PID: 14195 Comm: a.out Not tainted 6.0.0-rc6-dirty #863
>>   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>
> 
> Urgh, you hitting that WARN enough times to want to improve it seems to
> suggest your machine is quite sick.

My machine is not sick at all. I just wanted this hint for debugging
https://syzkaller.appspot.com/bug?extid=94cc2a66fc228b23f360 .

In a world of debugging without vmcore, printing as much hint as possible is
important. Therefore, WARN_ONCE() is more appreciated than WARN_ON_ONCE().

> 
> Anyway, patch is ok I suppose.

Thank you. Please send this patch and
https://lkml.kernel.org/r/9f42e8a5-f809-3f2c-0fda-b7657bc94eb3@I-love.SAKURA.ne.jp
via your tree.
[tip: locking/core] locking/lockdep: Print more debug information - report name and key when look_up_lock_class() got confused
Posted by tip-bot2 for Tetsuo Handa 3 years, 6 months ago 
The following commit has been merged into the locking/core branch of tip:

Commit-ID:     76e64c73db9542ff4bae8a60f4f32e38f3799b95
Gitweb:        https://git.kernel.org/tip/76e64c73db9542ff4bae8a60f4f32e38f3799b95
Author:        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
AuthorDate:    Mon, 19 Sep 2022 09:52:13 +09:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 21 Sep 2022 09:58:21 +02:00

locking/lockdep: Print more debug information - report name and key when look_up_lock_class() got confused

Printing this information will be helpful:

  ------------[ cut here ]------------
  Looking for class "l2tp_sock" with key l2tp_socket_class, but found a different class "slock-AF_INET6" with the same key
  WARNING: CPU: 1 PID: 14195 at kernel/locking/lockdep.c:940 look_up_lock_class+0xcc/0x140
  Modules linked in:
  CPU: 1 PID: 14195 Comm: a.out Not tainted 6.0.0-rc6-dirty #863
  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>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/bd99391e-f787-efe9-5ec6-3c6dc4c587b0@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 64a13eb..e3375bc 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__,
+				  "Looking for class \"%s\" with key %ps, but found a different class \"%s\" with the same key\n",
+				  lock->name, lock->key, class->name);
 			return class;
 		}
 	}

Patchew 2.1-devel-ea86937

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