Messages in this thread | | | Date | Thu, 22 Aug 2013 17:38:07 +0900 | From | Yoshihiro YUNOMAE <> | Subject | Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock |
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(2013/08/20 23:27), Don Zickus wrote: > On Tue, Aug 20, 2013 at 03:12:32AM -0700, Eric W. Biederman wrote: >> Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> writes: >> >>> Hi Ingo, >>> >>> Thank you for fixing typos! >>> OK, I'll fix them and rename to ioapic_zap_locks(). >>> >>> Thank you again! >> >> >> The better fix for this would be to remove the disable_IO_APIC call from >> crash_kexec. >> >> I know last time it was investigated the kernel was very close to >> working without needing that, and the code will be much more robust in >> the long term if we can avoid disabling them in the crashing kernel. >> >> Yoshihiro is there any chance you can look into removing the >> disable_IO_APIC entirely? >> >> The apic disablement and the disable_IO_APIC exists entirely due to >> limitations in the kernel boot path. > > Yup. We went down this path a year ago: > > https://lkml.org/lkml/2012/2/2/331 > > Then we got sidetracked and talked about removing the lapic stuff at > shutdown too: > > http://lists.infradead.org/pipermail/kexec/2012-February/006017.html > (sorry couldn't find lkml link for some reason) > > And the second patch was committed. > > However, it was quickly reverted when Yinghai Lu noticed a problem: > > https://lkml.org/lkml/2012/2/11/143 > > The problem stemmed from the fact that the nmi_watchdog caused an NMI in > the middle of transitioning between the two kernels (we didn't shutdown > the lapic) and caused a reset (there is no NMI handler in purgatory). > > I think I dropped the ball in investigating how to write an idt for the > purgatory code to handle spurious NMIs. > > Regardless of all that, I think if we stick to just removing the ioapic > shutdown code (ie the first patch linked above), we should be ok. I > believe my testing went smoothly. It was the lapic stuff that needed more > tweaking. > > So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep > the code simpler.
Thank you for commenting about my patch. I didn't know you already have submitted the patches for this deadlock problem.
I can't answer definitively right now that no problems are induced by removing disable_IO_APIC(). However, my patch should be work well (and has already been merged to -tip tree). So how about taking my patch at first, and then discussing the removal of disabled_IO_APIC()?
Thanks, Yoshihiro YUNOMAE
-- Yoshihiro YUNOMAE Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: yoshihiro.yunomae.ez@hitachi.com
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