On 22/02/2021 04:15, Alan Fisher wrote:
Hello,
I've been trying to get the evbmips port working on a new chip recently,
and in the process I've tried building the kernel with PARANOIA enabled.
This has resulted in a crash on startup, and I am wondering if it is
surfacing a bug. Here is what's happening:
Some code under an #ifdef PARANOIA in cpu_switchto checks whether the
IPL is IPL_SCHED, and if not, throws a trap. According to the manpage
for cpu_switchto(9), the current IPL level being IPL_SCHED is a
precondition for cpu_switchto(), so this check seems to make sense. The
callstack looks like this:
cpu_switchto - this causes a trap when the check fails - manpage says
IPL must be IPL_SCHED
mi_switch - manpage says IPL must be IPL_SCHED
yield - manpage doesn't say anything about IPL_SCHED, and IPL is not
changed in this routine
276 yield(void)
277 {
278 struct lwp *l = curlwp;
279
280 KERNEL_UNLOCK_ALL(l, &l->l_biglocks);
281 lwp_lock(l);
lwp_lock will raise the IPL to IPL_SCHED. spc_{lock,mutex} are used by
lwp_lock (maybe others)
HTH,
Nick
