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

Boqun Feng
2019-07-10T05:18:43Z

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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@gmail.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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