linux-kernel - Re: [RFC tip/locking/lockdep v5 04/17] lockdep: Introduce lock

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Date:   Sat, 24 Feb 2018 15:31:01 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Andrea Parri <parri.andrea@...il.com>
Subject: Re: [RFC tip/locking/lockdep v5 04/17] lockdep: Introduce
 lock_list::dep

On Sat, Feb 24, 2018 at 01:32:50PM +0800, Boqun Feng wrote:
[...]
> 
> I also reorder bit number for each kind of dependency, so that we have a
> simple __calc_dep_bit(), see the following:
> 
> 	/*
> 	 * DEP_*_BIT in lock_list::dep
> 	 *
> 	 * For dependency @prev -> @next:
> 	 *
> 	 *   RR: both @prev and @next are recursive read locks, i.e. ->read == 2.
> 	 *   RN: @prev is recursive and @next is non-recursive.
> 	 *   NR: @prev is a not recursive and @next is recursive.
> 	 *   NN: both @prev and @next are non-recursive.
> 	 * 
> 	 * Note that we define the value of DEP_*_BITs so that:
> 	 * 	bit0 is prev->read != 2
> 	 * 	bit1 is next->read != 2
> 	 */
> 	#define DEP_RR_BIT 0
> 	#define DEP_RN_BIT 1
> 	#define DEP_NR_BIT 2

Oops, to make the following __cal_dep_bit() works, we should have:

 	#define DEP_NR_BIT 1
 	#define DEP_RN_BIT 2

instead.

Regards,
Boqun

> 	#define DEP_NN_BIT 3
> 
> 	#define DEP_RR_MASK (1U << (DEP_RR_BIT))
> 	#define DEP_RN_MASK (1U << (DEP_RN_BIT))
> 	#define DEP_NR_MASK (1U << (DEP_NR_BIT))
> 	#define DEP_NN_MASK (1U << (DEP_NN_BIT))
> 
> 	static inline unsigned int
> 	__calc_dep_bit(struct held_lock *prev, struct held_lock *next)
> 	{
> 		return (prev->read != 2) + ((next->read != 2) << 1)
> 	}
> 
> 	static inline u8 calc_dep(struct held_lock *prev, struct held_lock *next)
> 	{
> 		return 1U << __calc_dep_bit(prev, next);
> 	}
> 

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