Re: [LKP] [tty] c96cf923a9: WARNING:possible_circular_locking_dependency_detected

[Waiman Long]

On 12/12/2018 12:04 AM, Sergey Senozhatsky wrote:
> On (12/12/18 12:42), Sergey Senozhatsky wrote:
> [..]
>>>>> [   87.255156]        CPU0                    CPU1
>>>>> [   87.255813]        ----                    ----
>>>>> [   87.256460]   lock(&port_lock_key);
>>>>> [   87.256973]                                lock(console_owner);
>>>>> [   87.257829]                                lock(&port_lock_key);
>>>>> [   87.258680]   lock(&obj_hash[i].lock);
>> So it's like
>>
>> 	CPU0					CPU1
>>
>> 	uart_shutdown()				db->lock
>> 	 uart_port->lock			 debug_print_object()
>> 	  free_page()				  printk
>> 	   debug_check_no_obj_freed		   uart_port->lock
>> 	    db->lock
>>
>>
>> In this particular case we probably can just move free_page()
>> out of uart_port lock scope. Note that free_page()->MM can printk()
>> on its own.
>>
> [..]
>> [1] https://lore.kernel.org/lkml/1542653726-5655-8-git-send-email-longman@xxxxxxxxxx/T/#u
> That said, I'd first try Waiman's patch. The one I suggested is
> more of a defense move - there are too many things happening under
> uart_port->lock. This is not the first time we see lockdep complaining
> about the way uart and the rest of the kernel interact.
>
> 	-ss

Thanks for the information. I will extract my debugobjects patch out of
my lockdep patchset and send it out as standalone patch.

Cheers,
Longman