ext4: recheck buffer uptodate bit under buffer lock

Commit 8e33fadf945a ("ext4: remove an unnecessary if statement in
__ext4_get_inode_loc()") forget to recheck buffer's uptodate bit again
under buffer lock, which may overwrite the buffer if someone else have
already brought it uptodate and changed it.

Fixes: 8e33fadf945a ("ext4: remove an unnecessary if statement in __ext4_get_inode_loc()")
Cc: [e-mail]
Signed-off-by: Zhang Yi <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Signed-off-by: Theodore Ts'o <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

fs/ext4/inode.c

···
 		goto has_buffer;
 
 	lock_buffer(bh);
+	if (ext4_buffer_uptodate(bh)) {
+		/* Someone brought it uptodate while we waited */
+		unlock_buffer(bh);
+		goto has_buffer;
+	}
+
 	/*
 	 * If we have all information of the inode in memory and this
 	 * is the only valid inode in the block, we need not read the