[sheepdog] [PATCH v3 3/5] work: protect nr_threads by wi->workers_lock

[Hitoshi Mitake]

From: Hitoshi Mitake <mitake.hitoshi at gmail.com>

Previous protection scheme of wi->nr_thread in work.c was
unclear because wi->startup_lock was also used for protecting it
during workqueue grow/shrink. This patch let work.c protect
wi->nr_thread by the new wi->workers_lock.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
---
 lib/work.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

v3:
 - add a new mutex for protecting nr_threads and procedure of wq grow/shrink

diff --git a/lib/work.c b/lib/work.c
index 84eb727..e973519 100644
--- a/lib/work.c
+++ b/lib/work.c
@@ -68,6 +68,9 @@ struct worker_info {
 	pthread_mutex_t pending_lock;
 	/* protected by pending_lock */
 	struct work_queue q;
+
+	pthread_mutex_t workers_lock;
+	/* protected by workers_lock */
 	size_t nr_threads;
 
 	/* protected by uatomic primitives */
@@ -145,18 +148,18 @@ static int create_worker_threads(struct worker_info *wi, size_t nr_threads)
 	pthread_t thread;
 	int ret;
 
-	pthread_mutex_lock(&wi->startup_lock);
+	pthread_mutex_lock(&wi->workers_lock);
 	while (wi->nr_threads < nr_threads) {
 		ret = pthread_create(&thread, NULL, worker_routine, wi);
 		if (ret != 0) {
 			sd_err("failed to create worker thread: %m");
-			pthread_mutex_unlock(&wi->startup_lock);
+			pthread_mutex_unlock(&wi->workers_lock);
 			return -1;
 		}
 		wi->nr_threads++;
 		sd_debug("create thread %s %zu", wi->name, wi->nr_threads);
 	}
-	pthread_mutex_unlock(&wi->startup_lock);
+	pthread_mutex_unlock(&wi->workers_lock);
 
 	return 0;
 }
@@ -293,7 +296,11 @@ static void *worker_routine(void *arg)
 
 		pthread_mutex_lock(&wi->pending_lock);
 		if (wq_need_shrink(wi)) {
+			pthread_mutex_unlock(&wi->pending_lock);
+
+			pthread_mutex_lock(&wi->workers_lock);
 			wi->nr_threads--;
+			pthread_mutex_unlock(&wi->workers_lock);
 
 #ifdef ENABLE_TRACE
 			pthread_mutex_lock(&tid_map_lock);
@@ -301,7 +308,6 @@ static void *worker_routine(void *arg)
 			pthread_mutex_unlock(&tid_map_lock);
 #endif
 
-			pthread_mutex_unlock(&wi->pending_lock);
 			pthread_detach(pthread_self());
 			sd_debug("destroy thread %s %d, %zu", wi->name, tid,
 				 wi->nr_threads);
-- 
1.7.10.4