[PATCH 0/3] Fix IO error reporting on fsync()

[Jan Kara]

  Hello,

  current code in buffer.c has two pitfalls that cause problems with IO
error reporting of filesystems using mapping->private_list for their
metadata buffers (e.g. ext2).
  The first problem is that end_io_async_write() does not mark IO error
in the buffer flags, only in the page flags. Hence fsync_buffers_list()
does not find out that some IO error has occured and will not report it.
  The second problem is that buffers from private_list can be freed
(e.g. under memory pressure) and if fsync_buffer_list() is called after
that moment, IO error is lost - note that metadata buffers mark AS_EIO
on the *device mapping* not on the inode mapping.
  Following series of three patches tries to fix these problems. The
approach I took (after some discussions with Andrew) is introducing
dummy buffer_head in the mapping instead of private_list. This dummy
buffer head serves as a head of metadata buffer list and also collects
IO errors from other buffers on the list (see the third patch for more
details). This is kind of compromise between introducing a pointer to
inode's address_space into each buffer and between using list_head
instead of buffer_head and playing some dirty tricks to recognize that
one particular list_head is actually from address_space and not from
buffer_head. Any suggestions for improvements welcome.

								Honza
-- 
Jan Kara <jack@xxxxxxx>
SuSE CR Labs
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