ext4: don't perform block validity checks on the journal inode

BugLink: https://bugs.launchpad.net/bugs/1878098

commit 0a944e8a upstream.

Since the journal inode is already checked when we added it to the
block validity's system zone, if we check it again, we'll just trigger
a failure.

This was causing failures like this:

[   53.897001] EXT4-fs error (device sda): ext4_find_extent:909: inode
#8: comm jbd2/sda-8: pblk 121667583 bad header/extent: invalid extent entries - magic f30a, entries 8, max 340(340), depth 0(0)
[   53.931430] jbd2_journal_bmap: journal block not found at offset 49 on sda-8
[   53.938480] Aborting journal on device sda-8.

... but only if the system was under enough memory pressure that
logical->physical mapping for the journal inode gets pushed out of the
extent cache.  (This is why it wasn't noticed earlier.)

Fixes: 345c0dbf ("ext4: protect journal inode's blocks using block_validity")
Reported-by: Dan Rue <dan.rue@linaro.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Ashwin H <ashwinh@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/ext4/extents.c

@@ -549,10 +549,14 @@ __read_extent_tree_block(const char *function, unsigned int line,
 	}
 	if (buffer_verified(bh) && !(flags & EXT4_EX_FORCE_CACHE))
 		return bh;
-	err = __ext4_ext_check(function, line, inode,
-			       ext_block_hdr(bh), depth, pblk);
-	if (err)
-		goto errout;
+	if (!ext4_has_feature_journal(inode->i_sb) ||
+	    (inode->i_ino !=
+	     le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_journal_inum))) {
+		err = __ext4_ext_check(function, line, inode,
+				       ext_block_hdr(bh), depth, pblk);
+		if (err)
+			goto errout;
+	}
 	set_buffer_verified(bh);
 	/*
 	 * If this is a leaf block, cache all of its entries