Re: [Xenomai-core] [PowerPC]Badness at mmu_context_nohash

[Philippe Gerum <rpm@xenomai.org>]

On Fri, 2011-04-29 at 18:08 +0200, Jean-Michel Hautbois wrote:
> 2011/4/29 Philippe Gerum <rpm@xenomai.org>:
> > On Thu, 2011-04-28 at 10:33 +0200, Jean-Michel Hautbois wrote:
> >> 2011/4/27 Philippe Gerum <rpm@xenomai.org>:
> >> > On Wed, 2011-04-27 at 20:42 +0200, Jean-Michel Hautbois wrote:
> >> >> Hi list,
> >> >>
> >> >> I am currently using a Xenomai port on a linux 2.6.35.11 linux kernel
> >> >> and the adeos-ipipe-2.6.35.7-powerpc-2.12-01.patch.
> >> >> I am facing a scheduling issue on a P2020 (dual core PowerPC), and I
> >> >> get the following message :
> >> >>
> >> >> Badness at arch/powerpc/mm/mmu_context_nohash.c:209
> >> >> NIP: c0018d20 LR: c039b94c CTR: c00343e4
> >> >> REGS: ecfadce0 TRAP: 0700   Tainted: G        W    (2.6.35.11)
> >> >> MSR: 00021000 <ME,CE>  CR: 24000488  XER: 00000000
> >> >> TASK = ec5220d0[496] 'sipaq' THREAD: ecfac000 CPU: 1
> >> >> GPR00: 00000001 ecfadd90 ec5220d0 ec5df340 ec58a700 00000000 ffffffff 00000003
> >> >> GPR08: c04a2d98 00000007 c04a2d98 0067e000 0002f385 1007f1f8 c04a5b40 ecfac040
> >> >> GPR16: c04a5b40 c04deb80 c04a2120 c04a2d98 c04a5b40 c04d008c ecfac000 00029000
> >> >> GPR24: c04d0000 c04d1e6c 00000001 ec58a700 eceaf390 c04d1e78 c0b23b40 ec5df340
> >> >> NIP [c0018d20] switch_mmu_context+0x80/0x438
> >> >> LR [c039b94c] schedule+0x774/0x7dc
> >> >> Call Trace:
> >> >> [ecfadd90] [44000484] 0x44000484 (unreliable)
> >> >> [ecfadde0] [c039b94c] schedule+0x774/0x7dc
> >> >> [ecfade50] [c039cb98] do_nanosleep+0xc8/0x114
> >> >> [ecfade80] [c0059bf8] hrtimer_nanosleep+0xd8/0x158
> >> >> [ecfadf10] [c0059d48] sys_nanosleep+0xd0/0xd4
> >> >> [ecfadf40] [c0013c0c] ret_from_syscall+0x0/0x3c
> >> >> --- Exception: c01 at 0xffa6cc4
> >> >>    LR = 0xffa6cb0
> >> >> Instruction dump:
> >> >> 40a2fff0 4c00012c 2f800000 409e0128 813b018c 2f830000 39290001 913b018c
> >> >> 419e0020 8003018c 7c000034 5400d97e <0f000000> 8123018c 3929ffff 9123018c
> >> >>
> >> >> Do you have a clue on how to start debugging it ?
> >> >
> >> > Yes, but that can't be easily summarized here. In short, we have a
> >> > serious problem with the sharing of the MMU context between the Linux
> >> > and Xenomai schedulers in the SMP case on powerpc.
> >>
> >> OK, good to know that it is a known issue. If there is a thread with
> >> some thoughts about it, I am interested ;).
> >>
> >> >> It is happening quite randomly... :).
> >> >
> >> > Does disabling CONFIG_XENO_HW_UNLOCKED_SWITCH clear this issue?
> >> >
> >>
> >> Well, yes and no. It starts well, but when booting the kernel I get :
> >
> >
> > The mm switch issue was specifically addressed by this patch, which is
> > part of 2.12-01:
> > http://git.denx.de/?p=ipipe-2.6.git;a=commit;h=c14a47630d62d0328de1957636dceb1d498f7048
> >
> > However, it the last 2.6.35 patch issued was based on 2.6.35.7, not
> > 2.6.35.11, so there is still the possibility that something went wrong
> > while you forward ported this code.
> >
> > - Please check that mmu_context_nohash.c does contain the fix above as
> > it should
> 
> It is ok, I have the fix.

Does 2.6.35.7-2.12-02 exhibit the issue as well?

> 
> > - Please try Richard's suggestion, i.e. moving to 2.6.36, which may give
> > us more hints.
> 
> It is better. I don't have the badness on mmu context anymore.
> This gives some hints ;).
> 

Yes and no. The mmu management code involved was untouched between
2.6.35 and 2.6.36, so I still don't get why this activity counter gets
trashed yet.

> >> Badness at kernel/lockdep.c:2327
> >> NIP: c006e554 LR: c006e53c CTR: 000186a0
> >
> > Adeos sometimes conflicts with the vanilla IRQ state tracer. I'll have a
> > look at this. Disable CONFIG_TRACE_IRQFLAGS.
> 
> Yes, but I *want* to have the CONFIG_TRACE_IRQFLAGS on. I just wanted
> to tell that I had the problem, in order to be sure it is known ;).
> 

Sure, but one issue at a time.

> JM

-- 
Philippe.