ext4: don't remount read-only with errors=continue on reboot

ext4_handle_error() with errors=continue mount option can accidentally
remount the filesystem read-only when the system is rebooting. Fix that.

Fixes: 1dc1097f ("ext4: avoid panic during forced reboot")
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@kernel.org
Link: https://lore.kernel.org/r/20201127113405.26867-2-jack@suse.czSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

@@ -666,19 +666,17 @@ static bool system_going_down(void)
 
 static void ext4_handle_error(struct super_block *sb)
 {
+	journal_t *journal = EXT4_SB(sb)->s_journal;
+
 	if (test_opt(sb, WARN_ON_ERROR))
 		WARN_ON_ONCE(1);
 
-	if (sb_rdonly(sb))
+	if (sb_rdonly(sb) || test_opt(sb, ERRORS_CONT))
 		return;
 
-	if (!test_opt(sb, ERRORS_CONT)) {
-		journal_t *journal = EXT4_SB(sb)->s_journal;
-
 	ext4_set_mount_flag(sb, EXT4_MF_FS_ABORTED);
 	if (journal)
 		jbd2_journal_abort(journal, -EIO);
-	}
 	/*
 	 * We force ERRORS_RO behavior when system is rebooting. Otherwise we
 	 * could panic during 'reboot -f' as the underlying device got already