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SubjectRe: Seeing "huh, entered softirq 8 ffffffff802682aa preempt_count 00000100, exited with 00010100?" in tip.git

* Ingo Molnar <mingo@elte.hu> wrote:

> >>> Call Trace:
> >>> [<ffffffff80238c1f>] __schedule_bug+0x62/0x66
> >>> [<ffffffff80211d2d>] ? retint_restore_args+0x5/0x20
> >>> [<ffffffff80503921>] __schedule+0x95/0x792
> >>> [<ffffffff802093aa>] ? _stext+0x3aa/0x1000
> >>> [<ffffffff802093aa>] ? _stext+0x3aa/0x1000
> >>> [<ffffffff805040c2>] schedule+0xe/0x22
> >>> [<ffffffff8020ff04>] cpu_idle+0x70/0x72
> >>> [<ffffffff804fc3a0>] cpu_bringup_and_idle+0x13/0x15
> >>> Creating initial device nodes
> >>> Setting up hotplug.
> >>>
> >>>
> >>> From what I can see, softirq 8 is the RCU softirq. I don't know if
> >>> the "scheduling while atomic" is related or not, but its two new
> >>> schedulerish symptoms appearing at once, so I think its likely
> >>> they're related.
> >>>
> >>
> >> Hmmm... Mysterious, as you seem to be using classic RCU, which hasn't
> >> changed in awhile. Which branch of the tip tree are you using?
> >>
> >
> > tip/master. It looks like this appeared since -rc1. Mu current
> > suspicion is the percpu changes, since I'm seeing some other strange
> > symptoms.
>
> Cc:-ed more folks - it's either the percpu changes or the APIC changes
> (both occured at about the same time). Or maybe something from upstream.

managed to bisect one of the boot crashes i've been seeing:

a698c823e15149941b0f0281527d0c0d1daf2639 is first bad commit
commit a698c823e15149941b0f0281527d0c0d1daf2639
Author: Tejun Heo <tj@kernel.org>
Date: Tue Jan 13 20:41:35 2009 +0900

x86: make vmlinux_32.lds.S use PERCPU() macro

Make vmlinux_32.lds.S use the generic PERCPU() macro instead of open
coding it. This will ease future changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

# bad: [b16884e8] Merge branch 'x86/urgent'
# good: [f2257b70] Merge git://git.kernel.org/pub/scm/linux/kernel/gi
# good: [345fa66b] Merge branch 'core/locking'
# bad: [f534caca] Merge branch 'oprofile'
# bad: [3eb3963f] Merge branch 'cpus4096' into core/percpu
# bad: [1b437c8c] x86-64: Move irq stats from PDA to per-cpu and con
# good: [54da5b3d] x86: fix broken flush_tlb_others_ipi(), fix
# good: [c2c21745] x86: replacing mp_config_intsrc with mpc_intsrc
# bad: [c8f3329a] x86: use static _cpu_pda array
# good: [7de6883f] x86: fix pda_to_op()
# bad: [a698c823] x86: make vmlinux_32.lds.S use PERCPU() macro
# good: [c90aa894] x86: cleanup early setup_percpu references

testing the revert now.

This might be similar to the other 32-bit linker bug that was tracked down
yesterday and reverted - maybe that revert unearthed a problem with this
commit?

Ingo


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