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SubjectRe: [PATCH v2 2/2] lockdep: Remove unnecessary acquisitions wrt workqueue flush
On Fri, Sep 08, 2017 at 05:46:25PM +0900, Byungchul Park wrote:
> The workqueue added manual acquisitions to catch deadlock cases.
> Now crossrelease was introduced, some of those are redundant, since
> wait_for_completion() already includes the acquisition for itself.
> Removed it.

Now, lock_map_acquire() is already embedded in wait_for_completion(),
manual acquisitions for the same purpose should be removed, since they
would be duplicated. Consider this, please.

> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> include/linux/workqueue.h | 4 ++--
> kernel/workqueue.c | 20 ++++----------------
> 2 files changed, 6 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index db6dc9d..1bef13e 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -218,7 +218,7 @@ static inline void destroy_delayed_work_on_stack(struct delayed_work *work) { }
> \
> __init_work((_work), _onstack); \
> (_work)->data = (atomic_long_t) WORK_DATA_INIT(); \
> - lockdep_init_map(&(_work)->lockdep_map, #_work, &__key, 0); \
> + lockdep_init_map(&(_work)->lockdep_map, "(complete)"#_work, &__key, 0); \
> INIT_LIST_HEAD(&(_work)->entry); \
> (_work)->func = (_func); \
> } while (0)
> @@ -398,7 +398,7 @@ enum {
> static struct lock_class_key __key; \
> const char *__lock_name; \
> \
> - __lock_name = #fmt#args; \
> + __lock_name = "(complete)"#fmt#args; \
> \
> __alloc_workqueue_key((fmt), (flags), (max_active), \
> &__key, __lock_name, ##args); \
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index ab3c0dc..72f68b1 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2497,15 +2497,8 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
> INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
> __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
>
> - /*
> - * Explicitly init the crosslock for wq_barrier::done, make its lock
> - * key a subkey of the corresponding work. As a result we won't
> - * build a dependency between wq_barrier::done and unrelated work.
> - */
> - lockdep_init_map_crosslock((struct lockdep_map *)&barr->done.map,
> - "(complete)wq_barr::done",
> - target->lockdep_map.key, 1);
> - __init_completion(&barr->done);
> + init_completion_with_map(&barr->done, &target->lockdep_map);
> +
> barr->task = current;
>
> /*
> @@ -2611,16 +2604,14 @@ void flush_workqueue(struct workqueue_struct *wq)
> struct wq_flusher this_flusher = {
> .list = LIST_HEAD_INIT(this_flusher.list),
> .flush_color = -1,
> - .done = COMPLETION_INITIALIZER_ONSTACK(this_flusher.done),
> };
> int next_color;
>
> + init_completion_with_map(&this_flusher.done, &wq->lockdep_map);
> +
> if (WARN_ON(!wq_online))
> return;
>
> - lock_map_acquire(&wq->lockdep_map);
> - lock_map_release(&wq->lockdep_map);
> -
> mutex_lock(&wq->mutex);
>
> /*
> @@ -2883,9 +2874,6 @@ bool flush_work(struct work_struct *work)
> if (WARN_ON(!wq_online))
> return false;
>
> - lock_map_acquire(&work->lockdep_map);
> - lock_map_release(&work->lockdep_map);
> -
> if (start_flush_work(work, &barr)) {
> wait_for_completion(&barr.done);
> destroy_work_on_stack(&barr.work);
> --
> 1.9.1

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