Messages in this thread | | | From | Frans Pop <> | Subject | Re: [BUG,2.6.28,s390] Fails to boot in Hercules S/390 emulator - hang traced | Date | Wed, 18 Mar 2009 13:07:42 +0100 |
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On Wednesday 18 March 2009, john stultz wrote: > In my testing, this isn't really specific to the recent rounding > change, however the rounding change made the issue crop up fast enough > that it could be seen, whereas before the issue wouldn't crop up before > the tod clock was installed. If you boot w/ clocksource=jiffies, you'll > probably see the hang with your working kernels as well, only at a > later point (it would be helpful if you would verify that and let me > know).
Confirmed. It then hangs while checking/loading the initramfs.
On Wednesday 18 March 2009, Martin Schwidefsky wrote: > From: Martin Schwidefsky <schwidefsky@de.ibm.com> > > The implementation of __div64_31 for G5 machines is broken. The > comments in __div64_31 are correct, only the code does not do what the > comments say. The part "If the remainder has overflown subtract base > and increase the quotient" is only partially realized, the base is > subtracted correctly but the quotient is only increased if the dividend > had the last bit set. Using the correct instruction fixes the problem. > > Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Reported-by: Frans Pop <elendil@planet.nl> Tested-by: Frans Pop <elendil@planet.nl>
I've tried this patch with 2.6.28.8 and it fixes the hang! Maybe that aspect should be mentioned in the commit log?
I've also tested the patch with 2.6.29-rc8 and it also fixes the hang during login I reported with that [1]. Which means that not only jiffies is affected, but also tod! And that does not really surprise me because after the system switches to tod, I also see a continuously increasing error with clock->xtime_nsec always equal to -4096 (see below).
Am I correct that any kernel starting from 2.6.19 is affected by this, and that it's the most likely cause of Debian bug report http://bugs.debian.org/511334? If so, I'll get it pushed into Debian's stable kernels.
Cheers, FJP
[1] http://marc.info/?t=123656370500001&r=1&w=2
Ever increasing error with tod on 2.6.28.8 (with Martin's patch applied): 0.672655! timekeeping: clock source changed from jiffies to tod (shift: 12) 0.676889! tod/12 (150): xtime.tv: 1237377507/55524946 -> 1237377507/55524947 0.677020! clock->xtime: 0 -> -4096, error: 0 -> -4294967296 0.680788! tod/12 (151): xtime.tv: 1237377507/55524947 -> 1237377507/55524948 0.680919! clock->xtime: -4096 -> -4096, error: -4294967296 -> -8589934592 0.685280! tod/12 (152): xtime.tv: 1237377507/55524948 -> 1237377507/55524949 0.685411! clock->xtime: -4096 -> -4096, error: -8589934592 -> -12884901888 4.685237! tod/12 (1152): xtime.tv: 1237377511/55525948 -> 1237377511/55525949 4.685356! clock->xtime: -4096 -> -4096, error: -4303557230592 -> -4307852197888 20.700920! tod/12 (5155): xtime.tv: 1237377527/55529951 -> 1237377527/55529952 20.701057! clock->xtime: -4096 -> -4096, error: -21496311316480 -> -21500606283776 32.864888! tod/12 (8160): xtime.tv: 1237377539/55532956 -> 1237377539/55532957 32.865008! clock->xtime: -4096 -> -4096, error: -34402688040960 -> -34406983008256 86.760987! tod/12 (21172): xtime.tv: 1237377593/55545968 -> 1237377593/55545969 86.761120! clock->xtime: -4096 -> -4096, error: -90288802496512 -> -90293097463808 127.100183! tod/12 (29180): xtime.tv: 1237377633/55553976 -> 1237377633/55553977 127.100304! clock->xtime: -4096 -> -4096, error: -124682900602880 -> -124687195570176 491.860765! tod/12 (37189): xtime.tv: 1237377998/55561985 -> 1237377998/55561986 491.860886! clock->xtime: -4096 -> -4096, error: -159081293676544 -> -159085588643840
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