linux-kernel - Re: Seeing "huh, entered softirq 8 ffffffff802682aa preempt_count 00000100, exited with 00010100?" in tip.git

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Date:	Fri, 30 Jan 2009 23:17:47 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>, Tejun Heo <tj@...nel.org>
Cc:	paulmck@...ux.vnet.ibm.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: Seeing "huh, entered softirq 8 ffffffff802682aa preempt_count
	00000100, exited with 00010100?" in tip.git


* Ingo Molnar <mingo@...e.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@...nel.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@...nel.org>
    Signed-off-by: Ingo Molnar <mingo@...e.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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