[PATCH 4.18 012/158] block: dont warn when doing fsync on read-only devices

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

commit 8b2ded1c94c06f841f8c1612bcfa33c85012a36b upstream.

It is possible to call fsync on a read-only handle (for example, fsck.ext2
does it when doing read-only check), and this call results in kernel
warning.

The patch b089cfd95d32 ("block: don't warn for flush on read-only device")
attempted to disable the warning, but it is buggy and it doesn't
(op_is_flush tests flags, but bio_op strips off the flags).

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Fixes: 721c7fc701c7 ("block: fail op_is_write() requests to read-only partitions")
Cc: stable@xxxxxxxxxxxxxxx	# 4.18
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 block/blk-core.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2161,9 +2161,12 @@ static inline bool bio_check_ro(struct b
 {
 	const int op = bio_op(bio);
 
-	if (part->policy && (op_is_write(op) && !op_is_flush(op))) {
+	if (part->policy && op_is_write(op)) {
 		char b[BDEVNAME_SIZE];
 
+		if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
+			return false;
+
 		WARN_ONCE(1,
 		       "generic_make_request: Trying to write "
 			"to read-only block-device %s (partno %d)\n",