Messages in this thread Patch in this message |  | | | From | Frans Pop <> | | Subject | Re: [BUG,2.6.28,s390] Fails to boot in Hercules S/390 emulator | | Date | Mon, 9 Mar 2009 16:04:53 +0100 |
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On Sunday 08 March 2009, Frans Pop wrote: > Kernels after 2.6.27 fail to boot in the Hercules S/390 emulator, quite > early in the boot process: [...] > 0.141419! Initializing cgroup subsys ns > 0.141605! Initializing cgroup subsys cpuacct > 0.142009! Initializing cgroup subsys devices > 0.180403! cpu: 2 configured CPUs, 0 standby CPUs > > I've bisected this to the following commit: > commit 5cd1c9c5cf30d4b33df3d3f74d8142f278d536b7 > Author: Roman Zippel <zippel@linux-m68k.org> > Date: Mon Sep 22 14:42:43 2008 -0700 > timekeeping: fix rounding problem during clock update
After staring at this commit for a while I decided to try the following patch: --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -547,5 +547,11 @@ void update_wall_time(void) * add the remainder to the error difference. */ xtime.tv_nsec = ((s64)clock->xtime_nsec >> clock->shift) + 1; + if (unlikely(clock->xtime_nsec < ((s64)xtime.tv_nsec << clock->shift))) { + printk("Negative result: %llu - %lld\n", + (unsigned long long)clock->xtime_nsec, + (long long)((s64)xtime.tv_nsec << clock->shift)); + BUG_ON(1); + } clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift); And that resulted in: 0.004175! Negative result: 166039808000 - 166039808256
So we're trying to stuff a negative value into an unsigned field, and I keep seeing on these lists that's a bad idea.
I'll leave it up to you how we get there, but could it possibly be the same kind of thing as corrected earlier today in Heiko Carsten's patch: http://lkml.org/lkml/2009/3/9/112 ?
Cheers, FJP
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