Re: [PATCH v2 1/2] Replace if statement with WARN_ON_ONCE() in cmci_rediscover().

From: Tang Chen
Date: Sun Oct 21 2012 - 22:11:29 EST

On 10/20/2012 12:40 AM, Borislav Petkov wrote:
On Fri, Oct 19, 2012 at 01:45:27PM +0800, Tang Chen wrote:
cmci_rediscover() is only called by the CPU_POST_DEAD event handler,
which means the corresponding cpu has already dead. As a result, it
won't be accessed in the for_each_online_cpu loop.
So, we could change the if(cpu == dying) statement into a WARN_ON_ONCE().

Signed-off-by: Tang Chen<tangchen@xxxxxxxxxxxxxx>
arch/x86/kernel/cpu/mcheck/mce_intel.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_intel.c b/arch/x86/kernel/cpu/mcheck/mce_intel.c
index 38e49bc..481d152 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_intel.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_intel.c
@@ -180,8 +180,8 @@ void cmci_rediscover(int dying)

for_each_online_cpu(cpu) {
- if (cpu == dying)
- continue;
+ WARN_ON_ONCE(cpu == dying);

Ok, I don't understand that:

we want to warn that the rediscovering is happening on a dying cpu?? And
before that, we simply jumped over it and didn't do the rediscovering
there? Why should we warn at all?

Hi Borislav,

As far as I know, cmci_rediscover() is only called in
mce_cpu_callback() to handle CPU_POST_DEAD event.

2362 if (action == CPU_POST_DEAD) {
2363 /* intentionally ignoring frozen here */
2364 cmci_rediscover(cpu);
2365 }

I didn't find anywhere else using this function. So I think the cpu
should be dead already when this function is called.

I don't why before we just jumped over it. But I think if we have an
online cpu == dying here, it must be wrong. So I think we should warn
it, not just jump over it.

Thanks. :)


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