[PATCH] taskstats_tgid_free: fix usage

taskstats_tgid_free() is called on copy_process's error path. This is wrong.

	IF (clone_flags & CLONE_THREAD)
		We should not clear ->signal->taskstats, current uses it,
		it probably has a valid accumulated info.
	ELSE
		taskstats_tgid_init() set ->signal->taskstats = NULL,
		there is nothing to free.

Move the callsite to __exit_signal(). We don't need any locking, entire
thread group is exiting, nobody should have a reference to soon to be
released ->signal.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>