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SubjectRe: [PATCH] x86: fix dummy apic read/write warning
[Yinghai Lu - Sat, Jun 06, 2009 at 03:16:38PM -0700]
| ingo got
| [ 0.000000] Using APIC driver default
| [ 0.000000] SMP: Allowing 1 CPUs, 0 hotplug CPUs
| [ 0.000000] Local APIC disabled by BIOS -- you can enable it with "lapic"
| [ 0.000000] APIC: disable apic facility
| [ 0.000000] ------------[ cut here ]------------
| [ 0.000000] WARNING: at arch/x86/kernel/apic/apic.c:254 native_apic_read_dummy+0x2d/0x3b()
| [ 0.000000] Hardware name: HP OmniBook PC
|
| we have wrong check in dummy read and write.
| [we only test on system that have APIC with "disableapic"...]
|
| Signed-off-by: yinghai Lu <yinghai@kernel.org>
|
| ---
| arch/x86/kernel/apic/apic.c | 4 ++--
| 1 file changed, 2 insertions(+), 2 deletions(-)
|
| Index: linux-2.6/arch/x86/kernel/apic/apic.c
| ===================================================================
| --- linux-2.6.orig/arch/x86/kernel/apic/apic.c
| +++ linux-2.6/arch/x86/kernel/apic/apic.c
| @@ -246,12 +246,12 @@ static int modern_apic(void)
| */
| static void native_apic_write_dummy(u32 reg, u32 v)
| {
| - WARN_ON_ONCE((cpu_has_apic || !disable_apic));
| + WARN_ON_ONCE((cpu_has_apic && !disable_apic));
| }
|
| static u32 native_apic_read_dummy(u32 reg)
| {
| - WARN_ON_ONCE((cpu_has_apic || !disable_apic));
| + WARN_ON_ONCE((cpu_has_apic && !disable_apic));
| return 0;
| }
|
|

No Yinghai, this is wrong. native_apic_write_dummy is not
admissible to be called after apic->write has been NOP'ified.

If a site calls for apic->write after apic_disable() it's
a plain *bug* in caller. So we should continute warning if
cpu_has_apic _or_ !disable_apic.

Though since for SMP compiled kernel we still rely on
apic->read the snippet is to be changed to (cpu_has_apic && !disable_apic)
indeed.

-- Cyrill


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