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Subject[PATCH 3/3] lockdep: Remove unnecessary acquisitions wrt workqueue flush
Date
Workqueue added manual acquisitions to catch deadlock cases. Now
crossrelease was introduced, some of those are redundant because
crossrelease-enabled wait_for_completeion() also does it. Removed it.

Also, lock_map_acquire() in process_one_work() is too strong for
that purpose. lock_map_acquire_might() is enough. Replaced it.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/workqueue.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ab3c0dc..8b728d1 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2091,8 +2091,8 @@ static void process_one_work(struct worker *worker, struct work_struct *work)

spin_unlock_irq(&pool->lock);

- lock_map_acquire(&pwq->wq->lockdep_map);
- lock_map_acquire(&lockdep_map);
+ lock_map_acquire_might(&pwq->wq->lockdep_map);
+ lock_map_acquire_might(&lockdep_map);
/*
* Strictly speaking we should mark the invariant state without holding
* any locks, that is, before these two lock_map_acquire()'s.
@@ -2504,7 +2504,7 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
*/
lockdep_init_map_crosslock((struct lockdep_map *)&barr->done.map,
"(complete)wq_barr::done",
- target->lockdep_map.key, 1);
+ target->lockdep_map.key, 0);
__init_completion(&barr->done);
barr->task = current;

@@ -2611,16 +2611,17 @@ 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;

+ lockdep_init_map_crosslock((struct lockdep_map *)&this_flusher.done.map,
+ "(complete)wq_flusher::done",
+ wq->lockdep_map.key, 0);
+ __init_completion(&this_flusher.done);
+
if (WARN_ON(!wq_online))
return;

- lock_map_acquire(&wq->lockdep_map);
- lock_map_release(&wq->lockdep_map);
-
mutex_lock(&wq->mutex);

/*
@@ -2883,9 +2884,6 @@ 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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