[PATCH 01/10 V2] workqueue: use manager lock only to protect worker_idr

Lai Jiangshan
2014-05-12T06:52:30Z

worker_idr is highly bound to managers and is always/only accessed in manager
lock context. So we don't need pool->lock for it.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
kernel/workqueue.c | 34 ++++++----------------------------
1 files changed, 6 insertions(+), 28 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c3f076f..d38d07c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -124,8 +124,7 @@ enum {
* cpu or grabbing pool->lock is enough for read access. If
* POOL_DISASSOCIATED is set, it's identical to L.
*
- * MG: pool->manager_mutex and pool->lock protected. Writes require both
- * locks. Reads can happen under either lock.
+ * M: pool->manager_mutex protected.
*
* PL: wq_pool_mutex protected.
*
@@ -164,7 +163,7 @@ struct worker_pool {
/* see manage_workers() for details on the two manager mutexes */
struct mutex manager_arb; /* manager arbitration */
struct mutex manager_mutex; /* manager exclusion */
- struct idr worker_idr; /* MG: worker IDs and iteration */
+ struct idr worker_idr; /* M: worker IDs and iteration */

struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* PL: unbound_pool_hash node */
@@ -340,16 +339,6 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
lockdep_is_held(&wq->mutex), \
"sched RCU or wq->mutex should be held")

-#ifdef CONFIG_LOCKDEP
-#define assert_manager_or_pool_lock(pool) \
- WARN_ONCE(debug_locks && \
- !lockdep_is_held(&(pool)->manager_mutex) && \
- !lockdep_is_held(&(pool)->lock), \
- "pool->manager_mutex or ->lock should be held")
-#else
-#define assert_manager_or_pool_lock(pool) do { } while (0)
-#endif
-
#define for_each_cpu_worker_pool(pool, cpu) \
for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0]; \
(pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
@@ -378,14 +367,14 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
* @wi: integer used for iteration
* @pool: worker_pool to iterate workers of
*
- * This must be called with either @pool->manager_mutex or ->lock held.
+ * This must be called with @pool->manager_mutex.
*
* The if/else clause exists only for the lockdep assertion and can be
* ignored.
*/
#define for_each_pool_worker(worker, wi, pool) \
idr_for_each_entry(&(pool)->worker_idr, (worker), (wi)) \
- if (({ assert_manager_or_pool_lock((pool)); false; })) { } \
+ if (({ lockdep_assert_held(&pool->manager_mutex); false; })) { } \
else

/**
@@ -1725,13 +1714,7 @@ static struct worker *create_worker(struct worker_pool *pool)
* ID is needed to determine kthread name. Allocate ID first
* without installing the pointer.
*/
- idr_preload(GFP_KERNEL);
- spin_lock_irq(&pool->lock);
-
- id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_NOWAIT);
-
- spin_unlock_irq(&pool->lock);
- idr_preload_end();
+ id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_KERNEL);
if (id < 0)
goto fail;

@@ -1773,18 +1756,13 @@ static struct worker *create_worker(struct worker_pool *pool)
worker->flags |= WORKER_UNBOUND;

/* successful, commit the pointer to idr */
- spin_lock_irq(&pool->lock);
idr_replace(&pool->worker_idr, worker, worker->id);
- spin_unlock_irq(&pool->lock);

return worker;

fail:
- if (id >= 0) {
- spin_lock_irq(&pool->lock);
+ if (id >= 0)
idr_remove(&pool->worker_idr, id);
- spin_unlock_irq(&pool->lock);
- }
kfree(worker);
return NULL;
}
--
1.7.4.4