linux-kernel - Re: reservation.h: build error with lockdep disabled

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Date:	Thu, 26 Nov 2015 07:23:17 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: reservation.h: build error with lockdep disabled

On Thu, Nov 26, 2015 at 01:43:40PM +0000, Russell King - ARM Linux wrote:
> As of 3c3b177a9369 ("reservation: add suppport for read-only access
> using rcu") linux/reservation.h uses lockdep macros:
> 
> +#define reservation_object_held(obj) lockdep_is_held(&(obj)->lock.base)
> 
> This results in build errors when lockdep is disabled as lockdep_is_held()
> is only available when lockdep is enabled.  This has been reported today
> to break the etnaviv kernel driver, which we're hoping to submit for 4.5.
> 
> As this gets used with rcu_dereference_protected(), eg:
> 
> static inline struct reservation_object_list *
> reservation_object_get_list(struct reservation_object *obj)
> {
>         return rcu_dereference_protected(obj->fence,
>                                          reservation_object_held(obj));
> }
> 
> I'm guessing that it's not going to be a simple case of making it always
> return true or always return false.
> 
> Any ideas how to solve this?

The usual approach is something like this:

#ifdef CONFIG_PROVE_LOCKING
#define reservation_object_held(obj) lockdep_is_held(&(obj)->lock.base)
#else
#define reservation_object_held(obj) true
#endif

							Thanx, Paul

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