[GFS2] Allow journal recovery on read-only mount

This patch allows gfs2 to perform journal recovery even if it is mounted
read-only. Strictly speaking, a read-only mount should not be writing to
the filesystem, but we do this only to perform journal recovery. A
read-only mount will fail if we don't recover the dirty journal. Also,
when gfs2 is used as a root filesystem, it will be mounted read-only
before being mounted read-write during the boot sequence. A failed
read-only mount will panic the machine during bootup.

Signed-off-by: Abhijith Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/recovery.c

@@ -504,13 +504,21 @@ int gfs2_recover_journal(struct gfs2_jdesc *jd)
 			if (!test_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags))
 				ro = 1;
 		} else {
-			if (sdp->sd_vfs->s_flags & MS_RDONLY)
-				ro = 1;
+			if (sdp->sd_vfs->s_flags & MS_RDONLY) {
+				/* check if device itself is read-only */
+				ro = bdev_read_only(sdp->sd_vfs->s_bdev);
+				if (!ro) {
+					fs_info(sdp, "recovery required on "
+						"read-only filesystem.\n");
+					fs_info(sdp, "write access will be "
+						"enabled during recovery.\n");
+				}
+			}
 		}
 
 		if (ro) {
-			fs_warn(sdp, "jid=%u: Can't replay: read-only FS\n",
-				jd->jd_jid);
+			fs_warn(sdp, "jid=%u: Can't replay: read-only block "
+				"device\n", jd->jd_jid);
 			error = -EROFS;
 			goto fail_gunlock_tr;
 		}