On Mon, Jul 10, 2023 at 05:19:35PM +0200, Mark Kettenis wrote:
> > Date: Mon, 10 Jul 2023 09:57:39 -0500
> > From: Scott Cheloha <scottchel...@gmail.com>
> >
> > On Mon, Jul 10, 2023 at 07:42:55AM -0600, Theo de Raadt wrote:
> > > I dare you to write the simplest fix for this, instead of a diff that
> > > scrolls by.
> >
> > This patch seems to work. Will need to bang on it for a few more days.
> >
> > 1. Disable gmoninit after sched_stop_scondary_cpus(). The secondary
> > CPUs have halted, so we aren't racing sysctl(2) on a secondary CPU.
> >
> > 2. Restore gmoninit between resume_mp() and sched_start_secondary_cpus().
> > The secondary CPUs are out of cpu_hatch(), which is probably where we
> > are crashing during resume. The secondary CPUs haven't started
> > scheduling yet, so we aren't racing sysctl(2).
>
> It is still a bit scary to have cpu_hatch() call _mcount() but I guess
> adding __attribute__((no_profile)) to all of the functions called by
> cpu_hatch() isn't really workable either.
>
> That said...
>
> > Index: subr_suspend.c
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/subr_suspend.c,v
> > retrieving revision 1.15
> > diff -u -p -r1.15 subr_suspend.c
> > --- subr_suspend.c 2 Jul 2023 19:02:27 -0000 1.15
> > +++ subr_suspend.c 10 Jul 2023 14:51:01 -0000
> > @@ -18,6 +18,7 @@
> >
> > #include <sys/param.h>
> > #include <sys/systm.h>
> > +#include <sys/atomic.h>
> > #include <sys/buf.h>
> > #include <sys/clockintr.h>
> > #include <sys/reboot.h>
> > @@ -100,6 +101,14 @@ top:
> > #ifdef MULTIPROCESSOR
> > sched_stop_secondary_cpus();
> > KASSERT(CPU_IS_PRIMARY(curcpu()));
> > +#endif
> > +#ifdef GPROF
> > + extern int gmoninit;
> > + int gmon_state = gmoninit;
>
> No variable declarations in the middle of functions please.
Yep, moved up.
> > + gmoninit = 0;
> > + membar_producer();
>
> Why are you messing with memory barriers here?
>
> > +#endif
> > +#ifdef MULTIPROCESSOR
> > sleep_mp();
> > #endif
> >
> > @@ -172,6 +181,12 @@ fail_suspend:
> > resume_randomness(rndbuf, rndbuflen);
> > #ifdef MULTIPROCESSOR
> > resume_mp();
> > +#endif
> > +#ifdef GPROF
> > + gmoninit = gmon_state;
> > + membar_producer();
>
> And here?
gmoninit is not volatile. I had this idea that I wanted the store to
be globally visible before proceeding. But you and Theo are telling
me I don't need the barrier. I'll take your word for it, dropped.
--
suspend/resume and hibernate/unhibernate still work with the revised
patch below.
Index: subr_suspend.c
===================================================================
RCS file: /cvs/src/sys/kern/subr_suspend.c,v
retrieving revision 1.15
diff -u -p -r1.15 subr_suspend.c
--- subr_suspend.c 2 Jul 2023 19:02:27 -0000 1.15
+++ subr_suspend.c 10 Jul 2023 15:30:22 -0000
@@ -26,6 +26,9 @@
#include <sys/mount.h>
#include <sys/syscallargs.h>
#include <dev/wscons/wsdisplayvar.h>
+#ifdef GPROF
+#include <sys/gmon.h>
+#endif
#ifdef HIBERNATE
#include <sys/hibernate.h>
#endif
@@ -49,6 +52,9 @@ sleep_state(void *v, int sleepmode)
extern int perflevel;
size_t rndbuflen;
char *rndbuf;
+#ifdef GPROF
+ int gmon_state;
+#endif
#if NSOFTRAID > 0
extern void sr_quiesce(void);
#endif
@@ -100,6 +106,12 @@ top:
#ifdef MULTIPROCESSOR
sched_stop_secondary_cpus();
KASSERT(CPU_IS_PRIMARY(curcpu()));
+#endif
+#ifdef GPROF
+ gmon_state = gmoninit;
+ gmoninit = 0;
+#endif
+#ifdef MULTIPROCESSOR
sleep_mp();
#endif
@@ -172,6 +184,11 @@ fail_suspend:
resume_randomness(rndbuf, rndbuflen);
#ifdef MULTIPROCESSOR
resume_mp();
+#endif
+#ifdef GPROF
+ gmoninit = gmon_state;
+#endif
+#ifdef MULTIPROCESSOR
sched_start_secondary_cpus();
#endif
vfs_stall(curproc, 0);
