pipe: take allocation and freeing of pipe_inode_info out of ->i_mutex

* new field - pipe->files; number of struct file over that pipe (all
  sharing the same inode, of course); protected by inode->i_lock.
* pipe_release() decrements pipe->files, clears inode->i_pipe when
  if the counter has reached 0 (all under ->i_lock) and, in that case,
  frees pipe after having done pipe_unlock()
* fifo_open() starts with grabbing ->i_lock, and either bumps pipe->files
  if ->i_pipe was non-NULL or allocates a new pipe (dropping and regaining
  ->i_lock) and rechecks ->i_pipe; if it's still NULL, inserts new pipe
  there, otherwise bumps ->i_pipe->files and frees the one we'd allocated.
  At that point we know that ->i_pipe is non-NULL and won't go away, so
  we can do pipe_lock() on it and proceed as we used to.  If we end up
  failing, decrement pipe->files and if it reaches 0 clear ->i_pipe and
  free the sucker after pipe_unlock().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index ad1a427b5267..59778e1c9c08 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -34,6 +34,7 @@ struct pipe_buffer {
  *	@tmp_page: cached released page
  *	@readers: number of current readers of this pipe
  *	@writers: number of current writers of this pipe
+ *	@files: number of struct file refering this pipe (protected by ->i_lock)
  *	@waiting_writers: number of writers blocked waiting for room
  *	@r_counter: reader counter
  *	@w_counter: writer counter
@@ -47,6 +48,7 @@ struct pipe_inode_info {
 	unsigned int nrbufs, curbuf, buffers;
 	unsigned int readers;
 	unsigned int writers;
+	unsigned int files;
 	unsigned int waiting_writers;
 	unsigned int r_counter;
 	unsigned int w_counter;