fork: use pidfd_prepare()

Stop open-coding get_unused_fd_flags() and anon_inode_getfile(). That's
brittle just for keeping the flags between both calls in sync. Use the
dedicated helper.

Message-Id: <20230327-pidfd-file-api-v1-2-5c0e9a3158e4@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/kernel/fork.c b/kernel/fork.c
index a34395b..67bec6f 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2376,21 +2376,12 @@ static __latent_entropy struct task_struct *copy_process(
         * if the fd table isn't shared).
         */
        if (clone_flags & CLONE_PIDFD) {
-               retval = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
+               /* Note that no task has been attached to @pid yet. */
+               retval = __pidfd_prepare(pid, O_RDWR | O_CLOEXEC, &pidfile);
                if (retval < 0)
                        goto bad_fork_free_pid;
-
                pidfd = retval;
 
-               pidfile = anon_inode_getfile("[pidfd]", &pidfd_fops, pid,
-                                             O_RDWR | O_CLOEXEC);
-               if (IS_ERR(pidfile)) {
-                       put_unused_fd(pidfd);
-                       retval = PTR_ERR(pidfile);
-                       goto bad_fork_free_pid;
-               }
-               get_pid(pid);   /* held by pidfile now */
-
                retval = put_user(pidfd, args->pidfd);
                if (retval)
                        goto bad_fork_put_pidfd;