linux-kernel - Re: [PATCH v3 17/30] locking/lockdep: Add read-write type for a lock dependency

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Message-ID: <20190710051830.GB14490@tardis>
Date:   Wed, 10 Jul 2019 13:18:30 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Yuyang Du <duyuyang@...il.com>
Cc:     peterz@...radead.org, will.deacon@....com, mingo@...nel.org,
        bvanassche@....org, ming.lei@...hat.com, frederic@...nel.org,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        longman@...hat.com, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v3 17/30] locking/lockdep: Add read-write type for a lock
 dependency

On Fri, Jun 28, 2019 at 05:15:15PM +0800, Yuyang Du wrote:
> Direct dependencies need to keep track of their read-write lock types.
> Two bit fields, which share the distance field, are added to lock_list
> struct so the types are stored there.
> 
> With a dependecy lock1 -> lock2, lock_type1 has the type for lock1 and
> lock_type2 has the type for lock2, where the values are one of the
> lock_type enums.
> 
> Signed-off-by: Yuyang Du <duyuyang@...il.com>
> ---
>  include/linux/lockdep.h  | 15 ++++++++++++++-
>  kernel/locking/lockdep.c | 25 +++++++++++++++++++++++--
>  2 files changed, 37 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index eb26e93..fd619ac 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -185,6 +185,8 @@ static inline void lockdep_copy_map(struct lockdep_map *to,
>  		to->class_cache[i] = NULL;
>  }
>  
> +#define LOCK_TYPE_BITS	2
> +
>  /*
>   * Every lock has a list of other locks that were taken after or before
>   * it as lock dependencies. These dependencies constitute a graph, which
> @@ -207,7 +209,17 @@ struct lock_list {
>  	struct list_head		chains;
>  	struct lock_class		*class[2];
>  	struct lock_trace		trace;
> -	int				distance;
> +
> +	/*
> +	 * The lock_type fields keep track of the lock type of this
> +	 * dependency.
> +	 *
> +	 * With L1 -> L2, lock_type1 stores the lock type of L1, and
> +	 * lock_type2 stores that of L2.
> +	 */
> +	unsigned int			lock_type1 : LOCK_TYPE_BITS,
> +					lock_type2 : LOCK_TYPE_BITS,

Bad names ;-) Maybe fw_dep_type and bw_dep_type? Which seems to be
aligned with the naming schema other functions.

Regards,
Boqun

> +					distance   : 32 - 2*LOCK_TYPE_BITS;
>  
>  	/*
>  	 * The parent field is used to implement breadth-first search.
> @@ -362,6 +374,7 @@ enum lock_type {
>  	LOCK_TYPE_WRITE		= 0,
>  	LOCK_TYPE_READ,
>  	LOCK_TYPE_RECURSIVE,
> +	NR_LOCK_TYPE,
>  };
>  
>  /*
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 3c97d71..1805017 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -1307,9 +1307,17 @@ static struct lock_list *alloc_list_entry(void)
>   */
>  static int add_lock_to_list(struct lock_class *lock1, struct lock_class *lock2,
>  			    unsigned long ip, int distance,
> -			    struct lock_trace *trace, struct lock_chain *chain)
> +			    struct lock_trace *trace, struct lock_chain *chain,
> +			    int lock_type1, int lock_type2)
>  {
>  	struct lock_list *entry;
> +
> +	/*
> +	 * The distance bit field in struct lock_list must be large
> +	 * enough to hold the maximum lock depth.
> +	 */
> +	BUILD_BUG_ON((1 << (32 - 2*LOCK_TYPE_BITS)) < MAX_LOCK_DEPTH);
> +
>  	/*
>  	 * Lock not present yet - get a new dependency struct and
>  	 * add it to the list:
> @@ -1322,6 +1330,8 @@ static int add_lock_to_list(struct lock_class *lock1, struct lock_class *lock2,
>  	entry->class[1] = lock2;
>  	entry->distance = distance;
>  	entry->trace = *trace;
> +	entry->lock_type1 = lock_type1;
> +	entry->lock_type2 = lock_type2;
>  
>  	/*
>  	 * Both allocation and removal are done under the graph lock; but
> @@ -1465,6 +1475,16 @@ static inline struct list_head *get_dep_list(struct lock_list *lock, int forward
>  	return &class->dep_list[forward];
>  }
>  
> +static inline int get_lock_type1(struct lock_list *lock)
> +{
> +	return lock->lock_type1;
> +}
> +
> +static inline int get_lock_type2(struct lock_list *lock)
> +{
> +	return lock->lock_type2;
> +}
> +
>  /*
>   * Forward- or backward-dependency search, used for both circular dependency
>   * checking and hardirq-unsafe/softirq-unsafe checking.
> @@ -2503,7 +2523,8 @@ static inline void inc_chains(void)
>  	 * dependency list of the previous lock <prev>:
>  	 */
>  	ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
> -			       next->acquire_ip, distance, trace, chain);
> +			       next->acquire_ip, distance, trace, chain,
> +			       prev->read, next->read);
>  	if (!ret)
>  		return 0;
>  
> -- 
> 1.8.3.1
> 

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