From: Jens Axboe <axboe@fb.com>
Date: Fri, 4 Dec 2015 20:15:36 +0000 (-0700)
Subject: workqueue: fix potential ABBA deadlock in stats summing
X-Git-Tag: fio-2.2.13~47
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=a6a3469ea8753a999b9bb9bea33299700d3094eb

workqueue: fix potential ABBA deadlock in stats summing

Signed-off-by: Jens Axboe <axboe@fb.com>
---

diff --git a/workqueue.c b/workqueue.c
index 27d1060c..7cd83bfd 100644
--- a/workqueue.c
+++ b/workqueue.c
@@ -217,13 +217,32 @@ static void sum_val(uint64_t *dst, uint64_t *src)
 }
 #endif
 
-static void sum_ddir(struct thread_data *dst, struct thread_data *src,
-		     enum fio_ddir ddir)
+static void pthread_double_unlock(pthread_mutex_t *lock1,
+				  pthread_mutex_t *lock2)
 {
 #ifndef CONFIG_SFAA
-	pthread_mutex_lock(&dst->io_wq.stat_lock);
-	pthread_mutex_lock(&src->io_wq.stat_lock);
+	pthread_mutex_unlock(lock1);
+	pthread_mutex_unlock(lock2);
 #endif
+}
+
+static void pthread_double_lock(pthread_mutex_t *lock1, pthread_mutex_t *lock2)
+{
+#ifndef CONFIG_SFAA
+	if (lock1 < lock2) {
+		pthread_mutex_lock(lock1);
+		pthread_mutex_lock(lock2);
+	} else {
+		pthread_mutex_lock(lock2);
+		pthread_mutex_lock(lock1);
+	}
+#endif
+}
+
+static void sum_ddir(struct thread_data *dst, struct thread_data *src,
+		     enum fio_ddir ddir)
+{
+	pthread_double_lock(&dst->io_wq.stat_lock, &src->io_wq.stat_lock);
 
 	sum_val(&dst->io_bytes[ddir], &src->io_bytes[ddir]);
 	sum_val(&dst->io_blocks[ddir], &src->io_blocks[ddir]);
@@ -231,10 +250,7 @@ static void sum_ddir(struct thread_data *dst, struct thread_data *src,
 	sum_val(&dst->this_io_bytes[ddir], &src->this_io_bytes[ddir]);
 	sum_val(&dst->bytes_done[ddir], &src->bytes_done[ddir]);
 
-#ifndef CONFIG_SFAA
-	pthread_mutex_unlock(&src->io_wq.stat_lock);
-	pthread_mutex_unlock(&dst->io_wq.stat_lock);
-#endif
+	pthread_double_unlock(&dst->io_wq.stat_lock, &src->io_wq.stat_lock);
 }
 
 static void update_accounting(struct submit_worker *sw)