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Subject[patch] x86, paravirt-spinlocks: fix boot hang (was: Re: [PATCH RFC 0/4] Paravirtual spinlocks)

* 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.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 2dd1ccd..faba669 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -7,10 +7,11 @@ extra-y := head_$(BITS).o head$(BITS).o head.o init_task.o vmlinu
CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE)

ifdef CONFIG_FTRACE
-# Do not profile debug utilities
+# Do not profile debug and lowlevel utilities
CFLAGS_REMOVE_tsc_64.o = -pg
CFLAGS_REMOVE_tsc_32.o = -pg
CFLAGS_REMOVE_rtc.o = -pg
+CFLAGS_REMOVE_paravirt.o = -pg
endif

#

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