Re: 2.6.18-rc3-g3b445eea BUG: warning at /usr/src/linux-git/kernel/cpu.c:51/unlock_cpu_hotplug()

On Fri, Aug 04, 2006 at 12:24:57PM -0700, Linus Torvalds wrote:

On Fri, 4 Aug 2006, Michal Piotrowski wrote:
This was reported
http://www.ussg.iu.edu/hypermail/linux/kernel/0607.3/1867.html
http://www.ussg.iu.edu/hypermail/linux/kernel/0608.0/0675.html

It's time to use git-bisect.

BUG: warning at /usr/src/linux-git/kernel/cpu.c:51/unlock_cpu_hotplug()

Ok, that really is a pretty scary thing. The warning happens if the lock
is released by somebody else than the person who took it. I don't _think_
that's supposed to happen, but with cpu hotplug locking being as
"creative" as it is, maybe it's valid.

I was planning on shutting the cpu hotplug warnings up for v2.6.18 - at
least the "lukewarm IQ" one for _taking_ the lock recursively. But I had
planned on leaving the unlock_cpu_hotplug() in place, since up until now
it hadn't triggered, and it really smells like a bug if it does.

[<c0132a04>] unlock_cpu_hotplug+0x2c/0x54
[<c013a2ec>] stop_machine_run+0x2e/0x34
[<c0135686>] sys_init_module+0x15a0/0x178a
[<c015b7b7>] do_sync_read+0xb6/0xf1
[<c0102d51>] sysenter_past_esp+0x56/0x79

DaveJ, any ideas?

Not really :-/
Whilst it's mentioned that the git-cpufreq.patch that was in -mm
made this happen, I really don't see anything in what you merged
yesterday that could explain any of this.

99% of the changes were to longhaul, so we can ignore those,
leaving just:

[CPUFREQ] return error when failing to set minfreq

Looks benign.

[CPUFREQ] Propagate acpi_processor_preregister_performance return value.

Shouldn't affect anything wrt hotplug

[CPUFREQ] [1/2] add __find_governor helper and clean up some error handling.
[CPUFREQ] [2/2] demand load governor modules.

Looks harmless to me, and those new functions don't show up
in any of those functions.

So I'm at a loss to explain why this made this bug suddenly appear, but
I don't think this is anything new. Fixing it however...
I'm looking at it, but I don't see anything obvious yet.

Dave

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