3.16.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <ty...@mit.edu>

commit 0a944e8a6c66ca04c7afbaa17e22bf208a8b37f0 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: 345c0dbf3a30 ("ext4: protect journal inode's blocks using 
block_validity")
Reported-by: Dan Rue <dan....@linaro.org>
Signed-off-by: Theodore Ts'o <ty...@mit.edu>
Tested-by: Naresh Kamboju <naresh.kamb...@linaro.org>
[bwh: Backported to 3.16: Use EXT4_HAS_COMPAT_FEATURE()]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -503,10 +503,15 @@ __read_extent_tree_block(const char *fun
        }
        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_COMPAT_FEATURE(inode->i_sb,
+                                    EXT4_FEATURE_COMPAT_HAS_JOURNAL) ||
+           (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

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