1 files changed, 12 insertions, 0 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index aa1aa2345235..033bc135a41f 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -547,5 +547,17 @@ page_cache_async_readahead(struct address_space *mapping,
 
         /* do read-ahead */
         ondemand_readahead(mapping, ra, filp, true, offset, req_size);
+
+#ifdef CONFIG_BLOCK
+        /*
+         * Normally the current page is !uptodate and lock_page() will be
+         * immediately called to implicitly unplug the device. However this
+         * is not always true for RAID conifgurations, where data arrives
+         * not strictly in their submission order. In this case we need to
+         * explicitly kick off the IO.
+         */
+        if (PageUptodate(page))
+                blk_run_backing_dev(mapping->backing_dev_info, NULL);
+#endif
 }
 EXPORT_SYMBOL_GPL(page_cache_async_readahead);