pid: move pidfd_get_pid() to pid.c

process_madvise syscall needs pidfd_get_pid function to translate pidfd to
pid so this patch move the function to kernel/pid.c.

Suggested-by: Alexander Duyck <[e-mail]>
Signed-off-by: Minchan Kim <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Reviewed-by: Suren Baghdasaryan <[e-mail]>
Reviewed-by: Alexander Duyck <[e-mail]>
Reviewed-by: Vlastimil Babka <[e-mail]>
Acked-by: Christian Brauner <[e-mail]>
Acked-by: David Rientjes <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Brian Geffon <[e-mail]>
Cc: Daniel Colascione <[e-mail]>
Cc: Joel Fernandes <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: John Dias <[e-mail]>
Cc: Kirill Tkhai <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Oleksandr Natalenko <[e-mail]>
Cc: Sandeep Patil <[e-mail]>
Cc: SeongJae Park <[e-mail]>
Cc: SeongJae Park <[e-mail]>
Cc: Shakeel Butt <[e-mail]>
Cc: Sonny Rao <[e-mail]>
Cc: Tim Murray <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Florian Weimer <[e-mail]>
Cc: <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/pid.h

···
 struct file;
 
 extern struct pid *pidfd_pid(const struct file *file);
+struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
 
 static inline struct pid *get_pid(struct pid *pid)
 {

kernel/exit.c

···
 	return retval;
 }
 
-static struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
-{
-	struct fd f;
-	struct pid *pid;
-
-	f = fdget(fd);
-	if (!f.file)
-		return ERR_PTR(-EBADF);
-
-	pid = pidfd_pid(f.file);
-	if (!IS_ERR(pid)) {
-		get_pid(pid);
-		*flags = f.file->f_flags;
-	}
-
-	fdput(f);
-	return pid;
-}
-
 static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
 			  int options, struct rusage *ru)
 {

kernel/pid.c

···
 	return idr_get_next(&ns->idr, &nr);
 }
 
+struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
+{
+	struct fd f;
+	struct pid *pid;
+
+	f = fdget(fd);
+	if (!f.file)
+		return ERR_PTR(-EBADF);
+
+	pid = pidfd_pid(f.file);
+	if (!IS_ERR(pid)) {
+		get_pid(pid);
+		*flags = f.file->f_flags;
+	}
+
+	fdput(f);
+	return pid;
+}
+
 /**
  * pidfd_create() - Create a new pid file descriptor.
  *