2 files changed, 28 insertions, 10 deletions

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 9ed9c955add7..2acda9cea0f9 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -395,6 +395,13 @@ struct cached_dev {
 	atomic_t		io_errors;
 	unsigned int		error_limit;
 	unsigned int		offline_seconds;
+
+	/*
+	 * Retry to update writeback_rate if contention happens for
+	 * down_read(dc->writeback_lock) in update_writeback_rate()
+	 */
+#define BCH_WBRATE_UPDATE_MAX_SKIPS	15
+	unsigned int		rate_update_retry;
 };
 
 enum alloc_reserve {
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index d138a2d73240..3f0ff3aab6f2 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -235,19 +235,27 @@ static void update_writeback_rate(struct work_struct *work)
 		return;
 	}
 
-	if (atomic_read(&dc->has_dirty) && dc->writeback_percent) {
-		/*
-		 * If the whole cache set is idle, set_at_max_writeback_rate()
-		 * will set writeback rate to a max number. Then it is
-		 * unncessary to update writeback rate for an idle cache set
-		 * in maximum writeback rate number(s).
-		 */
-		if (!set_at_max_writeback_rate(c, dc)) {
-			down_read(&dc->writeback_lock);
+	/*
+	 * If the whole cache set is idle, set_at_max_writeback_rate()
+	 * will set writeback rate to a max number. Then it is
+	 * unncessary to update writeback rate for an idle cache set
+	 * in maximum writeback rate number(s).
+	 */
+	if (atomic_read(&dc->has_dirty) && dc->writeback_percent &&
+	    !set_at_max_writeback_rate(c, dc)) {
+		do {
+			if (!down_read_trylock((&dc->writeback_lock))) {
+				dc->rate_update_retry++;
+				if (dc->rate_update_retry <=
+				    BCH_WBRATE_UPDATE_MAX_SKIPS)
+					break;
+				down_read(&dc->writeback_lock);
+				dc->rate_update_retry = 0;
+			}
 			__update_writeback_rate(dc);
 			update_gc_after_writeback(c);
 			up_read(&dc->writeback_lock);
-		}
+		} while (0);
 	}
 
 
@@ -1006,6 +1014,9 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc)
 	dc->writeback_rate_fp_term_high = 1000;
 	dc->writeback_rate_i_term_inverse = 10000;
 
+	/* For dc->writeback_lock contention in update_writeback_rate() */
+	dc->rate_update_retry = 0;
+
 	WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
 	INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
 }