sigsuspend 怎么会是原子性的，在kernel 2.6.11中

这个问题我也在stack overflow上问了
http://stackoverflow.com/questions/29838398/how-could-sys-sigsuspend-is-atomical-in-linux-kernel-2-6-11

"the sigsuspend() system call does not allow signals to be sent after unblocking and before the schedule() invocation, because other processes cannot grab the CPU during that time interval"

但是从代码上看spin_unlock_irq之后到schedule()之前完全可以被其他CPU抢占。这个原子操作怎么实现呢？

sys_sigsuspend(int history0, int history1, old_sigset_t mask)
{
struct pt_regs * regs = (struct pt_regs *) &history0;
sigset_t saveset;

    mask &= _BLOCKABLE;
    spin_lock_irq(&current->sighand->siglock);
    saveset = current->blocked;
    siginitset(&current->blocked, mask);
    recalc_sigpending();
    spin_unlock_irq(&current->sighand->siglock);

    regs->eax = -EINTR;
    while (1) {
            current->state = TASK_INTERRUPTIBLE;
            schedule();
            if (do_signal(regs, &saveset))                         
                           return -EINTR;
    }

}