From: Dave Kleikamp <dave.kleikamp@oracle.com>
Date: Tue, 22 Sep 2015 19:18:11 +0000 (-0500)
Subject: block: loop: don't enable direct-io unless the filesystem supports it
X-Git-Tag: v4.1.12-92~272^2
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=7cbfba44f6ca2d707ba45c96e5273d5b0b02f1dc;p=users%2Fjedix%2Flinux-maple.git

block: loop: don't enable direct-io unless the filesystem supports it

Commit 3ddce635 was over-aggressive and enabled direct-io in the loop
driver even if the underlying file system didn't support it. This
would cause a NULL dereference of aops->direct_IO.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
---

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7b326f2a95bf8..b967126d28e20 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -555,7 +555,10 @@ static inline void loop_update_dio(struct loop_device *lo)
 	/*
 	 * UEK kernel will use direct-io whenever possible
 	 */
-	__loop_update_dio(lo, 1);
+	struct address_space *mapping = lo->lo_backing_file->f_mapping;
+	bool supports_dio = mapping->a_ops->direct_IO != NULL;
+
+	__loop_update_dio(lo, supports_dio);
 }
 
 /*