pipe: refactor argument for account_pipe_buffers()

This is a preparatory patch for following work. account_pipe_buffers()
performs accounting in the 'user_struct'. There is no need to pass a
pointer to a 'pipe_inode_info' struct (which is then dereferenced to
obtain a pointer to the 'user' field). Instead, pass a pointer directly
to the 'user_struct'. This change is needed in preparation for a
subsequent patch that the fixes the limit checking in alloc_pipe_info()
(and the resulting code is a little more logical).

Link: http://lkml.kernel.org/r/7277bf8c-a6fc-4a7d-659c-f5b145c981ab@gmail.com
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: <socketpair@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Jens Axboe <axboe@fb.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/pipe.c

@@ -601,10 +601,10 @@ pipe_fasync(int fd, struct file *filp, int on)
 	return retval;
 }
 
-static void account_pipe_buffers(struct pipe_inode_info *pipe,
+static void account_pipe_buffers(struct user_struct *user,
                                  unsigned long old, unsigned long new)
 {
-	atomic_long_add(new - old, &pipe->user->pipe_bufs);
+	atomic_long_add(new - old, &user->pipe_bufs);
 }
 
 static bool too_many_pipe_buffers_soft(struct user_struct *user)
@@ -641,7 +641,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
 			pipe->r_counter = pipe->w_counter = 1;
 			pipe->buffers = pipe_bufs;
 			pipe->user = user;
-			account_pipe_buffers(pipe, 0, pipe_bufs);
+			account_pipe_buffers(user, 0, pipe_bufs);
 			mutex_init(&pipe->mutex);
 			return pipe;
 		}
@@ -656,7 +656,7 @@ void free_pipe_info(struct pipe_inode_info *pipe)
 {
 	int i;
 
-	account_pipe_buffers(pipe, pipe->buffers, 0);
+	account_pipe_buffers(pipe->user, pipe->buffers, 0);
 	free_uid(pipe->user);
 	for (i = 0; i < pipe->buffers; i++) {
 		struct pipe_buffer *buf = pipe->bufs + i;
@@ -1077,7 +1077,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
 			memcpy(bufs + head, pipe->bufs, tail * sizeof(struct pipe_buffer));
 	}
 
-	account_pipe_buffers(pipe, pipe->buffers, nr_pages);
+	account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);
 	pipe->curbuf = 0;
 	kfree(pipe->bufs);
 	pipe->bufs = bufs;