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 21:56:39 +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:

> 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.

Thanks,

	Ingo