Messages in this thread | | | Date | Sun, 9 Jul 2006 23:44:39 +0200 | From | Pavel Machek <> | Subject | Re: [BUG] APM resume breakage from 2.6.18-rc1 clocksource changes |
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On Sun 2006-07-09 22:58:31, Mikael Pettersson wrote: > On Fri, 7 Jul 2006 21:01:26 +0200 (MEST), I wrote: > >Kernel 2.6.18-rc1 broke resume from APM suspend (to RAM) > >on my old Dell Latitude CPi laptop. At resume the disk > >spins up and the screen gets lit, but there is no response > >to the keyboard, not even sysrq. All other system activity > >also appears to be halted. > > > >I did the obvious test of reverting apm.c to the 2.6.17 > >version and fixing up the fallout from the TIF_POLLING_NRFLAG > >changes, but it made no difference. So the problem must be > >somewhere else. > > I've traced the cause of this problem to the i386 time-keeping > changes in kernel 2.6.17-git11. What happens is that: > - The kernel autoselects TSC as my clocksource, which is > reasonable since it's a PentiumII. 2.6.17 also chose the TSC. > - Immediately after APM resumes (arch/i386/kernel/apm.c line > 1231 in 2.6.18-rc1) there is an interrupt from the PIT, > which takes us to kernel/timer.c:update_wall_time(). > - update_wall_time() does a clocksource_read() and computes > the offset from the previous read. However, the TSC was > reset by HW or BIOS during the APM suspend/resume cycle and > is now smaller than it was at the prevous read. On my machine, > the offset is 0xffffffd598e0a566 at this point, which appears > to throw update_wall_time() into a very very long loop.
Step 0: could we get some sanity checks into that loop? I'm pretty sure we'll face some TSCs going backwards... panic-king the box at that point is okay, but infinite loop is not... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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