block: don't warn when doing fsync on read-only devices

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@redhat.com>
Fixes: 721c7fc701c7 ("block: fail op_is_write() requests to read-only partitions")
Cc: stable@vger.kernel.org	# 4.18
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 4 insertions, 1 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index dee56c282efb..4dbc93f43b38 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2163,9 +2163,12 @@ static inline bool bio_check_ro(struct bio *bio, struct hd_struct *part)
 {
         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",