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Subject: Re: [PATCH v2] locking/rwsem: Add DEBUG_RWSEMS to look for
 lock/unlock mismatches
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
References: <1522091848-18426-1-git-send-email-longman@redhat.com>
 <20180327060655.25zjgqlgbfsp6b3p@gmail.com>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <72b8a73c-bfc0-5884-199d-349ee3311802@redhat.com>
Date:   Tue, 27 Mar 2018 09:59:53 -0400
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On 03/27/2018 02:06 AM, Ingo Molnar wrote:
> * Waiman Long <longman@redhat.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.

Cheers,
Longman