jbd2: fix data-race and null-ptr-deref in jbd2_journal_dirty_metadata()

Since handle->h_transaction may be a NULL pointer, so we should change it
to call is_handle_aborted(handle) first before dereferencing it.

And the following data-race was reported in my fuzzer:

==================================================================
BUG: KCSAN: data-race in jbd2_journal_dirty_metadata / jbd2_journal_dirty_metadata

write to 0xffff888011024104 of 4 bytes by task 10881 on cpu 1:
jbd2_journal_dirty_metadata+0x2a5/0x770 fs/jbd2/transaction.c:1556
__ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358
ext4_do_update_inode fs/ext4/inode.c:5220 [inline]
ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869
__ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074
ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103
....

read to 0xffff888011024104 of 4 bytes by task 10880 on cpu 0:
jbd2_journal_dirty_metadata+0xf2/0x770 fs/jbd2/transaction.c:1512
__ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358
ext4_do_update_inode fs/ext4/inode.c:5220 [inline]
ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869
__ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074
ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103
....

value changed: 0x00000000 -> 0x00000001
==================================================================

This issue is caused by missing data-race annotation for jh->b_modified.
Therefore, the missing annotation needs to be added.

Reported-by: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=de24c3fe3c4091051710
Fixes: 6e06ae88edae ("jbd2: speedup jbd2_journal_dirty_metadata()")
Signed-off-by: Jeongjun Park <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>
Cc: [e-mail]

fs/jbd2/transaction.c

···
 				jh->b_next_transaction == transaction);
 		spin_unlock(&jh->b_state_lock);
 	}
-	if (jh->b_modified == 1) {
+	if (data_race(jh->b_modified == 1)) {
 		/* If it's in our transaction it must be in BJ_Metadata list. */
 		if (data_race(jh->b_transaction == transaction &&
 		    jh->b_jlist != BJ_Metadata)) {
···
 		goto out;
 	}
 
-	journal = transaction->t_journal;
 	spin_lock(&jh->b_state_lock);
 
 	if (is_handle_aborted(handle)) {
···
 		ret = -EROFS;
 		goto out_unlock_bh;
 	}
+
+	journal = transaction->t_journal;
 
 	if (jh->b_modified == 0) {
 		/*