pipe: don't use ->i_mutex

now it can be done - put mutex into pipe_inode_info, use it instead
of ->i_mutex
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ocfs2/file.c

@@ -2465,8 +2465,7 @@ static ssize_t ocfs2_file_splice_write(struct pipe_inode_info *pipe,
 			out->f_path.dentry->d_name.len,
 			out->f_path.dentry->d_name.name, len);
 
-	if (pipe->inode)
-		mutex_lock_nested(&pipe->inode->i_mutex, I_MUTEX_PARENT);
+	pipe_lock(pipe);
 
 	splice_from_pipe_begin(&sd);
 	do {
@@ -2486,8 +2485,7 @@ static ssize_t ocfs2_file_splice_write(struct pipe_inode_info *pipe,
 	} while (ret > 0);
 	splice_from_pipe_end(pipe, &sd);
 
-	if (pipe->inode)
-		mutex_unlock(&pipe->inode->i_mutex);
+	pipe_unlock(pipe);
 
 	if (sd.num_spliced)
 		ret = sd.num_spliced;

fs/pipe.c

@@ -56,7 +56,7 @@ unsigned int pipe_min_size = PAGE_SIZE;
 static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
 {
 	if (pipe->inode)
-		mutex_lock_nested(&pipe->inode->i_mutex, subclass);
+		mutex_lock_nested(&pipe->mutex, subclass);
 }
 
 void pipe_lock(struct pipe_inode_info *pipe)
@@ -71,7 +71,7 @@ EXPORT_SYMBOL(pipe_lock);
 void pipe_unlock(struct pipe_inode_info *pipe)
 {
 	if (pipe->inode)
-		mutex_unlock(&pipe->inode->i_mutex);
+		mutex_unlock(&pipe->mutex);
 }
 EXPORT_SYMBOL(pipe_unlock);
 
@@ -777,6 +777,7 @@ struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
 			pipe->r_counter = pipe->w_counter = 1;
 			pipe->inode = inode;
 			pipe->buffers = PIPE_DEF_BUFFERS;
+			mutex_init(&pipe->mutex);
 			return pipe;
 		}
 		kfree(pipe);

include/linux/pipe_fs_i.h

@@ -27,6 +27,7 @@ struct pipe_buffer {
 
 /**
  *	struct pipe_inode_info - a linux kernel pipe
+ *	@mutex: mutex protecting the whole thing
  *	@wait: reader/writer wait point in case of empty/full pipe
  *	@nrbufs: the number of non-empty pipe buffers in this pipe
  *	@buffers: total number of buffers (should be a power of 2)
@@ -44,6 +45,7 @@ struct pipe_buffer {
  *	@bufs: the circular array of pipe buffers
  **/
 struct pipe_inode_info {
+	struct mutex mutex;
 	wait_queue_head_t wait;
 	unsigned int nrbufs, curbuf, buffers;
 	unsigned int readers;