ext4: always panic when errors=panic is specified

Before commit 014c9caa ("ext4: make ext4_abort() use
__ext4_error()"), the following series of commands would trigger a
panic:

1. mount /dev/sda -o ro,errors=panic test
2. mount /dev/sda -o remount,abort test

After commit 014c9caa, remounting a file system using the test
mount option "abort" will no longer trigger a panic.  This commit will
restore the behaviour immediately before commit 014c9caa.
(However, note that the Linux kernel's behavior has not been
consistent; some previous kernel versions, including 5.4 and 4.19
similarly did not panic after using the mount option "abort".)

This also makes a change to long-standing behaviour; namely, the
following series commands will now cause a panic, when previously it
did not:

1. mount /dev/sda -o ro,errors=panic test
2. echo test > /sys/fs/ext4/sda/trigger_fs_error

However, this makes ext4's behaviour much more consistent, so this is
a good thing.

Cc: stable@kernel.org
Fixes: 014c9caa ("ext4: make ext4_abort() use __ext4_error()")
Signed-off-by: NYe Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20210401081903.3421208-1-yebin10@huawei.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

@@ -667,9 +667,6 @@ static void ext4_handle_error(struct super_block *sb, bool force_ro, int error,
 			ext4_commit_super(sb);
 	}
 
-	if (sb_rdonly(sb) || continue_fs)
-		return;
-
 	/*
 	 * We force ERRORS_RO behavior when system is rebooting. Otherwise we
 	 * could panic during 'reboot -f' as the underlying device got already
@@ -679,6 +676,10 @@ static void ext4_handle_error(struct super_block *sb, bool force_ro, int error,
 		panic("EXT4-fs (device %s): panic forced after error\n",
 			sb->s_id);
 	}
+
+	if (sb_rdonly(sb) || continue_fs)
+		return;
+
 	ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
 	/*
 	 * Make sure updated value of ->s_mount_flags will be visible before