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Subject[PATCH 3/7] workqueue: better define locking rules around worker creation / destruction
Date
When a manager creates or destroys workers, the operations are always
done with the manager_mutex held; however, initial worker creation or
worker destruction during pool release don't grab the mutex. They are
still correct as initial worker creation doesn't require
synchronization and grabbing manager_arb provides enough exclusion for
pool release path.

Still, let's make everyone follow the same rules for consistency and
such that lockdep annotations can be added.

Update create_and_start_worker() and put_unbound_pool() to grab
manager_mutex around thread creation and destruction respectively and
add lockdep assertions to create_worker() and destroy_worker().

This patch doesn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index cac7106..ce1ab06 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1715,6 +1715,8 @@ static struct worker *create_worker(struct worker_pool *pool)
struct worker *worker = NULL;
int id = -1;

+ lockdep_assert_held(&pool->manager_mutex);
+
spin_lock_irq(&pool->lock);
while (ida_get_new(&pool->worker_ida, &id)) {
spin_unlock_irq(&pool->lock);
@@ -1796,12 +1798,14 @@ static void start_worker(struct worker *worker)
* create_and_start_worker - create and start a worker for a pool
* @pool: the target pool
*
- * Create and start a new worker for @pool.
+ * Grab the managership of @pool and create and start a new worker for it.
*/
static int create_and_start_worker(struct worker_pool *pool)
{
struct worker *worker;

+ mutex_lock(&pool->manager_mutex);
+
worker = create_worker(pool);
if (worker) {
spin_lock_irq(&pool->lock);
@@ -1809,6 +1813,8 @@ static int create_and_start_worker(struct worker_pool *pool)
spin_unlock_irq(&pool->lock);
}

+ mutex_unlock(&pool->manager_mutex);
+
return worker ? 0 : -ENOMEM;
}

@@ -1826,6 +1832,9 @@ static void destroy_worker(struct worker *worker)
struct worker_pool *pool = worker->pool;
int id = worker->id;

+ lockdep_assert_held(&pool->manager_mutex);
+ lockdep_assert_held(&pool->lock);
+
/* sanity check frenzy */
if (WARN_ON(worker->current_work) ||
WARN_ON(!list_empty(&worker->scheduled)))
@@ -3531,6 +3540,7 @@ static void put_unbound_pool(struct worker_pool *pool)
* manager_mutex.
*/
mutex_lock(&pool->manager_arb);
+ mutex_lock(&pool->manager_mutex);
spin_lock_irq(&pool->lock);

while ((worker = first_worker(pool)))
@@ -3538,6 +3548,7 @@ static void put_unbound_pool(struct worker_pool *pool)
WARN_ON(pool->nr_workers || pool->nr_idle);

spin_unlock_irq(&pool->lock);
+ mutex_unlock(&pool->manager_mutex);
mutex_unlock(&pool->manager_arb);

/* shut down the timers */
--
1.8.1.4


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