diff mbox series

watchdog: Fix lockdep warning

Message ID ZNZr0mPsIuqKzb5u@p100 (mailing list archive)
State Superseded, archived
Headers show
Series watchdog: Fix lockdep warning | expand

Commit Message

Helge Deller Aug. 11, 2023, 5:11 p.m. UTC 
Fully initialize detector_work work struct to avoid this kernel warning
when lockdep is enabled:

 =====================================
 WARNING: bad unlock balance detected!
 6.5.0-rc5+ #687 Not tainted
 -------------------------------------
 swapper/0/1 is trying to release lock (detector_work) at:
 [<000000004037e554>] __flush_work+0x60/0x658
 but there are no more locks to release!

 other info that might help us debug this:
 no locks held by swapper/0/1.

 stack backtrace:
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc5+ #687
 Hardware name: 9000/785/C3700
 Backtrace:
  [<0000000041455d5c>] print_unlock_imbalance_bug.part.0+0x20c/0x230
  [<000000004040d5e8>] lock_release+0x2e8/0x3f8
  [<000000004037e5cc>] __flush_work+0xd8/0x658
  [<000000004037eb7c>] flush_work+0x30/0x60
  [<000000004011f140>] lockup_detector_check+0x54/0x128
  [<0000000040306430>] do_one_initcall+0x9c/0x408
  [<0000000040102d44>] kernel_init_freeable+0x688/0x7f0
  [<000000004146df68>] kernel_init+0x64/0x3a8
  [<0000000040302020>] ret_from_kernel_thread+0x20/0x28

Signed-off-by: Helge Deller <deller@gmx.de>

---

Comments

Petr Mladek Aug. 15, 2023, 11:54 a.m. UTC | #1 
Adding workqueue and lockdep people into Cc.

On Fri 2023-08-11 19:11:46, Helge Deller wrote:
> Fully initialize detector_work work struct to avoid this kernel warning
> when lockdep is enabled:
> 
>  =====================================
>  WARNING: bad unlock balance detected!
>  6.5.0-rc5+ #687 Not tainted
>  -------------------------------------
>  swapper/0/1 is trying to release lock (detector_work) at:
>  [<000000004037e554>] __flush_work+0x60/0x658
>  but there are no more locks to release!
> 
>  other info that might help us debug this:
>  no locks held by swapper/0/1.
> 
>  stack backtrace:
>  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc5+ #687
>  Hardware name: 9000/785/C3700
>  Backtrace:
>   [<0000000041455d5c>] print_unlock_imbalance_bug.part.0+0x20c/0x230
>   [<000000004040d5e8>] lock_release+0x2e8/0x3f8
>   [<000000004037e5cc>] __flush_work+0xd8/0x658
>   [<000000004037eb7c>] flush_work+0x30/0x60
>   [<000000004011f140>] lockup_detector_check+0x54/0x128
>   [<0000000040306430>] do_one_initcall+0x9c/0x408
>   [<0000000040102d44>] kernel_init_freeable+0x688/0x7f0
>   [<000000004146df68>] kernel_init+0x64/0x3a8
>   [<0000000040302020>] ret_from_kernel_thread+0x20/0x28
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> 
> ---
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index be38276a365f..eab0dfcfa3f9 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -1022,5 +1022,6 @@ void __init lockup_detector_init(void)
>  	else
>  		allow_lockup_detector_init_retry = true;
> 
> +	INIT_WORK(&detector_work, lockup_detector_delay_init);
>  	lockup_detector_setup();
>  }

Strange. The work is initialized when declared:

static struct work_struct detector_work __initdata =
		__WORK_INITIALIZER(detector_work, lockup_detector_delay_init);

, which should initialize the lockdep map as well. I would expect
this is enough.

And I do not see this on x86_64 with CONFIG_PROVE_LOCKING=y
on today's Linus' tree. And the flush_work() is always called
from the lockup_detector_check() late init call.

IMHO, it must be a bug somewhere else. Otherwise, many other
users of DECLARE_WORK() or __WORK_INITIALIZER() would have
the same problem.

Or do I miss something?

Best Regards,
Petr
Helge Deller Aug. 15, 2023, 12:44 p.m. UTC | #2 
On 8/15/23 13:54, Petr Mladek wrote:
> Adding workqueue and lockdep people into Cc.
>
> On Fri 2023-08-11 19:11:46, Helge Deller wrote:
>> Fully initialize detector_work work struct to avoid this kernel warning
>> when lockdep is enabled:
>>
>>   =====================================
>>   WARNING: bad unlock balance detected!
>>   6.5.0-rc5+ #687 Not tainted
>>   -------------------------------------
>>   swapper/0/1 is trying to release lock (detector_work) at:
>>   [<000000004037e554>] __flush_work+0x60/0x658
>>   but there are no more locks to release!
>>
>>   other info that might help us debug this:
>>   no locks held by swapper/0/1.
>>
>>   stack backtrace:
>>   CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc5+ #687
>>   Hardware name: 9000/785/C3700
>>   Backtrace:
>>    [<0000000041455d5c>] print_unlock_imbalance_bug.part.0+0x20c/0x230
>>    [<000000004040d5e8>] lock_release+0x2e8/0x3f8
>>    [<000000004037e5cc>] __flush_work+0xd8/0x658
>>    [<000000004037eb7c>] flush_work+0x30/0x60
>>    [<000000004011f140>] lockup_detector_check+0x54/0x128
>>    [<0000000040306430>] do_one_initcall+0x9c/0x408
>>    [<0000000040102d44>] kernel_init_freeable+0x688/0x7f0
>>    [<000000004146df68>] kernel_init+0x64/0x3a8
>>    [<0000000040302020>] ret_from_kernel_thread+0x20/0x28
>>
>> Signed-off-by: Helge Deller <deller@gmx.de>
>>
>> ---
>>
>> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
>> index be38276a365f..eab0dfcfa3f9 100644
>> --- a/kernel/watchdog.c
>> +++ b/kernel/watchdog.c
>> @@ -1022,5 +1022,6 @@ void __init lockup_detector_init(void)
>>   	else
>>   		allow_lockup_detector_init_retry = true;
>>
>> +	INIT_WORK(&detector_work, lockup_detector_delay_init);
>>   	lockup_detector_setup();
>>   }
>
> Strange. The work is initialized when declared:
>
> static struct work_struct detector_work __initdata =
> 		__WORK_INITIALIZER(detector_work, lockup_detector_delay_init);
>
> , which should initialize the lockdep map as well. I would expect
> this is enough.

Right. It's enough...

> And I do not see this on x86_64 with CONFIG_PROVE_LOCKING=y
> on today's Linus' tree. And the flush_work() is always called
> from the lockup_detector_check() late init call.
>
> IMHO, it must be a bug somewhere else. Otherwise, many other
> users of DECLARE_WORK() or __WORK_INITIALIZER() would have
> the same problem.

Right. I should have replied earlier to this patch.
Andrew already dropped this patch here from his patch collection.

It turns out the problem is in function static_obj() from
lockdep, which doesn't recognize the __initdata section
for all platforms.

Please look at this patch on the LKML instead, which
fixes the real problem:
[PATCH v2] lockdep: Fix static memory detection even more

Thanks!
Helge
diff mbox series

Patch

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index be38276a365f..eab0dfcfa3f9 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -1022,5 +1022,6 @@  void __init lockup_detector_init(void)
 	else
 		allow_lockup_detector_init_retry = true;

+	INIT_WORK(&detector_work, lockup_detector_delay_init);
 	lockup_detector_setup();
 }