linux-kernel - Re: [PATCH v2] locking/rwsem: Add DEBUG_RWSEMS to look for lock/unlock mismatches

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Message-ID: <529e4373-754e-307c-6dc2-a605a05826de@redhat.com>
Date:   Tue, 27 Mar 2018 16:37:34 -0400
From:   Waiman Long <longman@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] locking/rwsem: Add DEBUG_RWSEMS to look for
 lock/unlock mismatches

On 03/27/2018 03:56 PM, Ingo Molnar wrote:
> * Waiman Long <longman@...hat.com> wrote:
>
>> On 03/27/2018 02:06 AM, Ingo Molnar wrote:
>>> * Waiman Long <longman@...hat.com> wrote:
>>>
>>>> For a rwsem, locking can either be exclusive or shared. The corresponding
>>>> exclusive or shared unlock must be used. Otherwise, the protected data
>>>> structures may get corrupted or the lock may be in an inconsistent state.
>>>>
>>>> In order to detect such anomaly, a new configuration option DEBUG_RWSEMS
>>>> is added which can be enabled to look for such mismatches and print
>>>> warnings that that happens.
>>>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>>>> index 64155e3..0958192 100644
>>>> --- a/lib/Kconfig.debug
>>>> +++ b/lib/Kconfig.debug
>>>> @@ -1075,6 +1075,13 @@ config DEBUG_WW_MUTEX_SLOWPATH
>>>>  	 even a debug kernel.  If you are a driver writer, enable it.  If
>>>>  	 you are a distro, do not.
>>>>  
>>>> +config DEBUG_RWSEMS
>>>> +	bool "RW Semaphore debugging: basic checks"
>>>> +	depends on DEBUG_KERNEL && RWSEM_SPIN_ON_OWNER
>>>> +	help
>>>> +	  This feature allows mismatched rw semaphore locks and unlocks
>>>> +	  to be detected and reported.
>>>> +
>>> Makes sense - but this should also be integrated into the rest of lock debugging 
>>> Kconfig hierarchy similar to DEBUG_MUTEXES: i.e. DEBUG_LOCK_ALLOC, PROVE_LOCKING, 
>>> etc. should select this new lock debugging option as well.
>>>
>>> People generally are not supposed to know and configure the finer details, 
>>> CONFIG_LOCK_DEBUGGING=y is a one-stop-shop in this regard.
>> I can add a patch to rework lock debugging configuration code. Do you
>> want to hide the individual config options but still allow them to be
>> enabled manually? Alternatively we can also just add a master lock
>> debugging option to select them all.
> They should work like mutex debugging: it's auto-selected by PROVE_LOCKING, but 
> can be enabled individually as well if PROVE_LOCKING is disabled.
Got it.

Thanks,
Longman