[PATCH] pipe_rdwr_fasync: fix the error handling to prevent the leak/crash

[Oleg Nesterov <oleg@redhat.com>]

If the second fasync_helper() fails, pipe_rdwr_fasync() returns the error
but leaves the file on ->fasync_readers.

This was always wrong, but since 233e70f4228e78eb2f80dc6650f65d3ae3dbf17c
"saner FASYNC handling on file close" we have the new problem. Because in
this case setfl() doesn't set FASYNC bit, __fput() will not do ->fasync(0),
and we leak fasync_struct with ->fa_file pointing to the freed file.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

--- CUR/fs/pipe.c~PIPE_FASYNC	2009-01-12 23:07:47.000000000 +0100
+++ CUR/fs/pipe.c	2009-01-18 03:51:41.000000000 +0100
@@ -699,12 +699,13 @@ pipe_rdwr_fasync(int fd, struct file *fi
 	int retval;
 
 	mutex_lock(&inode->i_mutex);
-
 	retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
 
-	if (retval >= 0)
+	if (retval >= 0) {
 		retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
-
+		if (retval < 0) /* this can happen only if on == T */
+			fasync_helper(-1, filp, 0, &pipe->fasync_readers);
+	}
 	mutex_unlock(&inode->i_mutex);
 
 	if (retval < 0)