Re: Check in cpu_switchto triggering crash with PARANOIA on

Oh I see. Thanks for the help.

Looks like the check should be spl < IPL_SCHED instead of spl != IPL_SCHED. Seems it's just that the check is bad after all.

Index: arch/mips/mips/locore.S
===================================================================
RCS file: /cvsroot/src/sys/arch/mips/mips/locore.S,v
retrieving revision 1.226
diff -u -r1.226 locore.S
--- arch/mips/mips/locore.S 26 Sep 2020 08:21:10 -0000 1.226
+++ arch/mips/mips/locore.S 22 Feb 2021 09:49:27 -0000
@@ -224,7 +224,7 @@
PTR_L v0, L_CPU(MIPS_CURLWP)
INT_L v1, CPU_INFO_CPL(v0)
#if __mips >= 32
- tnei v1, IPL_SCHED
+ tltiu v1, IPL_SCHED
#else
li v0, IPL_SCHED
10: bne v0, v1, 10b

On Sun, Feb 21, 2021 at 11:22 PM Nick Hudson <nick.hudson%gmx.co.uk@localhost> wrote:

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