introduce variants of pipe_lock/pipe_unlock for real pipes/FIFOs

fs/pipe.c file_operations methods *know* that pipe is not an internal one;
no need to check pipe->inode for those callers.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/pipe.c

@@ -75,6 +75,16 @@ void pipe_unlock(struct pipe_inode_info *pipe)
 }
 EXPORT_SYMBOL(pipe_unlock);
 
+static inline void __pipe_lock(struct pipe_inode_info *pipe)
+{
+	mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
+}
+
+static inline void __pipe_unlock(struct pipe_inode_info *pipe)
+{
+	mutex_unlock(&pipe->mutex);
+}
+
 void pipe_double_lock(struct pipe_inode_info *pipe1,
 		      struct pipe_inode_info *pipe2)
 {
@@ -376,7 +386,7 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
 
 	do_wakeup = 0;
 	ret = 0;
-	pipe_lock(pipe);
+	__pipe_lock(pipe);
 	for (;;) {
 		int bufs = pipe->nrbufs;
 		if (bufs) {
@@ -464,7 +474,7 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
 		}
 		pipe_wait(pipe);
 	}
-	pipe_unlock(pipe);
+	__pipe_unlock(pipe);
 
 	/* Signal writers asynchronously that there is more room. */
 	if (do_wakeup) {
@@ -500,7 +510,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 
 	do_wakeup = 0;
 	ret = 0;
-	pipe_lock(pipe);
+	__pipe_lock(pipe);
 
 	if (!pipe->readers) {
 		send_sig(SIGPIPE, current, 0);
@@ -647,7 +657,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 		pipe->waiting_writers--;
 	}
 out:
-	pipe_unlock(pipe);
+	__pipe_unlock(pipe);
 	if (do_wakeup) {
 		wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM);
 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
@@ -667,7 +677,7 @@ static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 	switch (cmd) {
 		case FIONREAD:
-			pipe_lock(pipe);
+			__pipe_lock(pipe);
 			count = 0;
 			buf = pipe->curbuf;
 			nrbufs = pipe->nrbufs;
@@ -675,7 +685,7 @@ static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 				count += pipe->bufs[buf].len;
 				buf = (buf+1) & (pipe->buffers - 1);
 			}
-			pipe_unlock(pipe);
+			__pipe_unlock(pipe);
 
 			return put_user(count, (int __user *)arg);
 		default:
@@ -721,7 +731,7 @@ pipe_release(struct inode *inode, struct file *file)
 	struct pipe_inode_info *pipe = inode->i_pipe;
 	int kill = 0;
 
-	pipe_lock(pipe);
+	__pipe_lock(pipe);
 	if (file->f_mode & FMODE_READ)
 		pipe->readers--;
 	if (file->f_mode & FMODE_WRITE)
@@ -738,7 +748,7 @@ pipe_release(struct inode *inode, struct file *file)
 		kill = 1;
 	}
 	spin_unlock(&inode->i_lock);
-	pipe_unlock(pipe);
+	__pipe_unlock(pipe);
 
 	if (kill)
 		__free_pipe_info(pipe);
@@ -752,7 +762,7 @@ pipe_fasync(int fd, struct file *filp, int on)
 	struct pipe_inode_info *pipe = filp->private_data;
 	int retval = 0;
 
-	pipe_lock(pipe);
+	__pipe_lock(pipe);
 	if (filp->f_mode & FMODE_READ)
 		retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
 	if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {
@@ -761,7 +771,7 @@ pipe_fasync(int fd, struct file *filp, int on)
 			/* this can happen only if on == T */
 			fasync_helper(-1, filp, 0, &pipe->fasync_readers);
 	}
-	pipe_unlock(pipe);
+	__pipe_unlock(pipe);
 	return retval;
 }
 
@@ -1040,7 +1050,7 @@ static int fifo_open(struct inode *inode, struct file *filp)
 	filp->private_data = pipe;
 	/* OK, we have a pipe and it's pinned down */
 
-	pipe_lock(pipe);
+	__pipe_lock(pipe);
 
 	/* We can only do regular read/write on fifos */
 	filp->f_mode &= (FMODE_READ | FMODE_WRITE);
@@ -1110,7 +1120,7 @@ static int fifo_open(struct inode *inode, struct file *filp)
 	}
 
 	/* Ok! */
-	pipe_unlock(pipe);
+	__pipe_unlock(pipe);
 	return 0;
 
 err_rd:
@@ -1132,7 +1142,7 @@ static int fifo_open(struct inode *inode, struct file *filp)
 		kill = 1;
 	}
 	spin_unlock(&inode->i_lock);
-	pipe_unlock(pipe);
+	__pipe_unlock(pipe);
 	if (kill)
 		__free_pipe_info(pipe);
 	return ret;
@@ -1248,7 +1258,7 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 	if (!pipe)
 		return -EBADF;
 
-	pipe_lock(pipe);
+	__pipe_lock(pipe);
 
 	switch (cmd) {
 	case F_SETPIPE_SZ: {
@@ -1277,7 +1287,7 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 	}
 
 out:
-	pipe_unlock(pipe);
+	__pipe_unlock(pipe);
 	return ret;
 }