[PATCH 0/5] splice: locking changes and code refactoring

[Al Viro]

On Mon, Jan 13, 2014 at 06:14:16AM -0800, Christoph Hellwig wrote:
> ping?  Would be nice to get this into 3.14

Umm...  The reason for pipe_lock outside of ->i_mutex is this:
default_file_splice_write() calls splice_from_pipe() with
write_pipe_buf for callback.  splice_from_pipe() calls that
callback under pipe_lock(pipe).  And write_pipe_buf() calls
__kernel_write(), which certainly might want to take ->i_mutex.

Now, this codepath isn't taken for files that have non-NULL
->splice_write(), so that's not an issue for XFS and OCFS2,
but having pipe_lock nest between the ->i_mutex for filesystems
that do and do not have ->splice_write()...  Ouch...