more signal locking bugs?

[Martin J. Bligh]

task_lock nests *inside* tasklist_lock but ... :

__do_SAK:

	task_lock
	...
	send_sig (SIGKILL, ...)
		send_sig_info (SIGKILL, ...)
			if (T(sig, SIG_KERNEL_BROADCAST_MASK)))
				read_lock(&tasklist_lock);
				...
				read_unlock(&tasklist_lock);
	...
	task_unlock

#define SIG_KERNEL_BROADCAST_MASK (\
        M(SIGHUP)    |  M(SIGINT)    |  M(SIGQUIT)   |  M(SIGILL)    | \
        M(SIGTRAP)   |  M(SIGABRT)   |  M(SIGBUS)    |  M(SIGFPE)    | \
        M(SIGKILL)   |  M(SIGUSR1)   |  M(SIGSEGV)   |  M(SIGUSR2)   | \
        M(SIGPIPE)   |  M(SIGALRM)   |  M(SIGTERM)   |  M(SIGXCPU)   | \
        M(SIGXFSZ)   |  M(SIGVTALRM) |  M(SIGPROF)   |  M(SIGPOLL)   | \
        M(SIGSYS)    |  M_SIGSTKFLT  |  M(SIGPWR)    |  M(SIGCONT)   | \
        M(SIGSTOP)   |  M(SIGTSTP)   |  M(SIGTTIN)   |  M(SIGTTOU)   | \
        M_SIGEMT )