Re: [PATCH v5 01/13] lockdep: Refactor lookup_chain_cache()

Boqun Feng
2017-01-19T09:16:04Z

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On Wed, Jan 18, 2017 at 10:17:27PM +0900, Byungchul Park wrote:
> Currently, lookup_chain_cache() provides both 'lookup' and 'add'
> functionalities in a function. However, each is useful. So this
> patch makes lookup_chain_cache() only do 'lookup' functionality and
> makes add_chain_cahce() only do 'add' functionality. And it's more
> readable than before.
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> kernel/locking/lockdep.c | 129 +++++++++++++++++++++++++++++------------------
> 1 file changed, 81 insertions(+), 48 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 4d7ffc0..f37156f 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -2109,15 +2109,9 @@ static int check_no_collision(struct task_struct *curr,
> return 1;
> }
>
> -/*
> - * Look up a dependency chain. If the key is not present yet then
> - * add it and return 1 - in this case the new dependency chain is
> - * validated. If the key is already hashed, return 0.
> - * (On return with 1 graph_lock is held.)
> - */

I think you'd better put some comments here for the behavior of
add_chain_cache(), something like:

/*
* Add a dependency chain into chain hashtable.
*
* Must be called with graph_lock held.
* Return 0 if fail to add the chain, and graph_lock is released.
* Return 1 with graph_lock held if succeed.
*/

Regards,
Boqun

> -static inline int lookup_chain_cache(struct task_struct *curr,
> - struct held_lock *hlock,
> - u64 chain_key)
> +static inline int add_chain_cache(struct task_struct *curr,
> + struct held_lock *hlock,
> + u64 chain_key)
> {
> struct lock_class *class = hlock_class(hlock);
> struct hlist_head *hash_head = chainhashentry(chain_key);
> @@ -2125,49 +2119,18 @@ static inline int lookup_chain_cache(struct task_struct *curr,
> int i, j;
>
> /*
> + * Allocate a new chain entry from the static array, and add
> + * it to the hash:
> + */
> +
> + /*
> * We might need to take the graph lock, ensure we've got IRQs
> * disabled to make this an IRQ-safe lock.. for recursion reasons
> * lockdep won't complain about its own locking errors.
> */
> if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> return 0;
[...]

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