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SubjectRe: [patch] x86, paravirt-spinlocks: fix boot hang
Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
>
>
>> the patches caused a boot hang with this config:
>>
>> http://redhat.com/~mingo/misc/config-Wed_Jul__9_14_47_04_CEST_2008.bad
>>
>
> ok, fixed it via the patch below.
>
> Ingo
>
> -------------->
> commit 6412367fe22dc54cc727e7bec5bd65c36c1a0754
> Author: Ingo Molnar <mingo@elte.hu>
> Date: Wed Jul 9 15:42:09 2008 +0200
>
> x86, paravirt-spinlocks: fix boot hang
>
> the paravirt-spinlock patches caused a boot hang with this config:
>
> http://redhat.com/~mingo/misc/config-Wed_Jul__9_14_47_04_CEST_2008.bad
>
> i have bisected it down to:
>
> | commit e17b58c2e85bc2ad2afc07fb8d898017c2b75ed1
> | Author: Jeremy Fitzhardinge <jeremy@goop.org>
> | Date: Mon Jul 7 12:07:53 2008 -0700
> |
> | xen: implement Xen-specific spinlocks
>
> i.e. applying that patch alone causes the hang. The hang happens in the
> ftrace self-test:
>
> initcall utsname_sysctl_init+0x0/0x19 returned 0 after 0 msecs
> calling init_sched_switch_trace+0x0/0x4c
> Testing tracer sched_switch: PASSED
> initcall init_sched_switch_trace+0x0/0x4c returned 0 after 167 msecs
> calling init_function_trace+0x0/0x12
> Testing tracer ftrace:
> [hard hang]
>
> it should have continued like this:
>
> Testing tracer ftrace: PASSED
> initcall init_function_trace+0x0/0x12 returned 0 after 198 msecs
> calling init_irqsoff_tracer+0x0/0x14
> Testing tracer irqsoff: PASSED
> initcall init_irqsoff_tracer+0x0/0x14 returned 0 after 3 msecs
> calling init_mmio_trace+0x0/0x12
> initcall init_mmio_trace+0x0/0x12 returned 0 after 0 msecs
>
> the problem is that such lowlevel primitives as spinlocks should never
> be built with -pg (which ftrace does). Marking paravirt.o as non-pg and
> marking all spinlock ops as always-inline solve the hang.
>

Thanks Ingo, that would have taken me a while to work out.

Presumably that means that xen/smp.o should also be built without -pg.
In fact, should I move the spinlock code into its own file, so that
ftrace can cover as much as it can?

J


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