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

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Date:   Tue, 27 Mar 2018 08:06:55 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Waiman Long <longman@...hat.com>
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


* 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.

Thanks,

	Ingo