f2fs: fix to check readonly condition correctly

With below case, it can mount multi-device image w/ rw option, however
one of secondary device is set as ro, later update will cause panic, so
let's introduce f2fs_dev_is_readonly(), and check multi-devices rw status
in f2fs_remount() w/ it in order to avoid such inconsistent mount status.

mkfs.f2fs -c /dev/zram1 /dev/zram0 -f
blockdev --setro /dev/zram1
mount -t f2fs dev/zram0 /mnt/f2fs
mount: /mnt/f2fs: WARNING: source write-protected, mounted read-only.
mount -t f2fs -o remount,rw mnt/f2fs
dd if=/dev/zero  of=/mnt/f2fs/file bs=1M count=8192

kernel BUG at fs/f2fs/inline.c:258!
RIP: 0010:f2fs_write_inline_data+0x23e/0x2d0 [f2fs]
Call Trace:
  f2fs_write_single_data_page+0x26b/0x9f0 [f2fs]
  f2fs_write_cache_pages+0x389/0xa60 [f2fs]
  __f2fs_write_data_pages+0x26b/0x2d0 [f2fs]
  f2fs_write_data_pages+0x2e/0x40 [f2fs]
  do_writepages+0xd3/0x1b0
  __writeback_single_inode+0x5b/0x420
  writeback_sb_inodes+0x236/0x5a0
  __writeback_inodes_wb+0x56/0xf0
  wb_writeback+0x2a3/0x490
  wb_do_writeback+0x2b2/0x330
  wb_workfn+0x6a/0x260
  process_one_work+0x270/0x5e0
  worker_thread+0x52/0x3e0
  kthread+0xf4/0x120
  ret_from_fork+0x29/0x50

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/f2fs.h

@@ -4430,6 +4430,11 @@ static inline bool f2fs_hw_is_readonly(struct f2fs_sb_info *sbi)
 	return false;
 }
 
+static inline bool f2fs_dev_is_readonly(struct f2fs_sb_info *sbi)
+{
+	return f2fs_sb_has_readonly(sbi) || f2fs_hw_is_readonly(sbi);
+}
+
 static inline bool f2fs_lfs_mode(struct f2fs_sb_info *sbi)
 {
 	return F2FS_OPTION(sbi).fs_mode == FS_MODE_LFS;

fs/f2fs/super.c

@@ -2288,7 +2288,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	if (f2fs_readonly(sb) && (*flags & SB_RDONLY))
 		goto skip;
 
-	if (f2fs_sb_has_readonly(sbi) && !(*flags & SB_RDONLY)) {
+	if (f2fs_dev_is_readonly(sbi) && !(*flags & SB_RDONLY)) {
 		err = -EROFS;
 		goto restore_opts;
 	}