In do_writepages, if the value returned by ext4_writepages is "-ENOMEM"
and "wbc->sync_mode == WB_SYNC_ALL", retry until the condition is not met.

In __ext4_get_inode_loc, if the bh returned by sb_getblk is NULL,
the function returns -ENOMEM.

In __getblk_slow, if the return value of grow_buffers is less than 0,
the function returns NULL.

When the three processes are connected in series like the following stack,
an infinite loop may occur:

do_writepages					<--- keep retrying
 ext4_writepages
  mpage_map_and_submit_extent
   mpage_map_one_extent
    ext4_map_blocks
     ext4_ext_map_blocks
      ext4_ext_handle_unwritten_extents
       ext4_ext_convert_to_initialized
        ext4_split_extent
         ext4_split_extent_at
          __ext4_ext_dirty
           __ext4_mark_inode_dirty
            ext4_reserve_inode_write
             ext4_get_inode_loc
              __ext4_get_inode_loc		<--- return -ENOMEM
               sb_getblk
                __getblk_gfp
                 __getblk_slow			<--- return NULL
                  grow_buffers
                   grow_dev_page		<--- return -ENXIO
                    ret = (block < end_block) ? 1 : -ENXIO;

In this issue, bg_inode_table_hi is overwritten as an incorrect value.
As a result, `block < end_block` cannot be met in grow_dev_page.
Therefore, __ext4_get_inode_loc always returns '-ENOMEM' and do_writepages
keeps retrying. As a result, the writeback process is in the D state due
to an infinite loop.

Add a check on inode table block in the __ext4_get_inode_loc function by
referring to ext4_read_inode_bitmap to avoid this infinite loop.

Cc: stable@kernel.org
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20220817132701.3015912-3-libaokun1@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>