copy_process:
// holds tasklist_lock + ->siglock
       /*
        * inherit ioprio
        */
       p->ioprio = current->ioprio;

Why?  ->ioprio was already copied in dup_task_struct().  I guess this is
needed to ensure that the child can't escape
sys_ioprio_set(IOPRIO_WHO_{PGRP,USER}), yes?

In that case we don't need ->siglock held, and the comment should be
updated.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>