[PATCH v3] Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU

[PATCH v3] Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU

[Chen Yucong]

mces_seen is a Per-CPU variable which should only be accessed by Per-CPU as possible. So the
clear operation of mces_seen should also be local to Per-CPU rather than monarch CPU.

Meanwhile, there is also a potential risk that mces_seen will not be be cleared if a timeout
occurs in mce_end for monarch CPU. As a result, the stale value of mces_seen will reappear
on the next mce.

Based on the above reasons, this patch distribute the clear operation of mces_seen to Per-CPU
rather than only monarch CPU.

* From v1
 * Add Reviewed-by: Andi Kleen
 * Put the clear operation of mces_seen before the MCG_STATUS write.

* From v2
 * Fix some misspelling in the patch message. 

Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Chen Yucong <slaoub@gmail.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c |   18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 68317c8..966a5f5 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -785,13 +785,6 @@ static void mce_reign(void)
 	 */
 	if (global_worst <= MCE_KEEP_SEVERITY && mca_cfg.tolerant < 3)
 		mce_panic("Machine check from unknown source", NULL, NULL);
-
-	/*
-	 * Now clear all the mces_seen so that they don't reappear on
-	 * the next mce.
-	 */
-	for_each_possible_cpu(cpu)
-		memset(&per_cpu(mces_seen, cpu), 0, sizeof(struct mce));
 }
 
 static atomic_t global_nwo;
@@ -1137,9 +1130,6 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 		}
 	}
 
-	/* mce_clear_state will clear *final, save locally for use later */
-	m = *final;
-
 	if (!no_way_out)
 		mce_clear_state(toclear);
 
@@ -1161,7 +1151,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 			mce_panic("Fatal machine check on current CPU", &m, msg);
 		if (worst == MCE_AR_SEVERITY) {
 			/* schedule action before return to userland */
-			mce_save_info(m.addr, m.mcgstatus & MCG_STATUS_RIPV);
+			mce_save_info(final->addr, final->mcgstatus & MCG_STATUS_RIPV);
 			set_thread_flag(TIF_MCE_NOTIFY);
 		} else if (kill_it) {
 			force_sig(SIGBUS, current);
@@ -1170,6 +1160,12 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 
 	if (worst > 0)
 		mce_report_event(regs);
+
+	/*
+	 * Now clear the mces_seen of current CPU -*final - so that it does not
+	 * reappear on the next mce.
+	 */
+	memset(final, 0, sizeof(struct mce));
 	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
 out:
 	atomic_dec(&mce_entry);
-- 
1.7.10.4




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Re: [PATCH v3] Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU

[Naoya Horiguchi]

On Thu, May 22, 2014 at 08:32:20AM +0800, Chen Yucong wrote:
> mces_seen is a Per-CPU variable which should only be accessed by Per-CPU as possible. So the
> clear operation of mces_seen should also be local to Per-CPU rather than monarch CPU.
> 
> Meanwhile, there is also a potential risk that mces_seen will not be be cleared if a timeout
> occurs in mce_end for monarch CPU. As a result, the stale value of mces_seen will reappear
> on the next mce.
> 
> Based on the above reasons, this patch distribute the clear operation of mces_seen to Per-CPU
> rather than only monarch CPU.
> 
> * From v1
>  * Add Reviewed-by: Andi Kleen
>  * Put the clear operation of mces_seen before the MCG_STATUS write.
> 
> * From v2
>  * Fix some misspelling in the patch message. 
> 
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Chen Yucong <slaoub@gmail.com>

This patch is purely x86_64 MCE related matter, so you need add proper
recipients to be properly reviewed.
Personally I'm OK for this code change (it reduces the processing time of
monarch CPU somewhat, I think it's a small benefit), but you got complainments
in ver.2, so please make some consensus.

And please fix misspelling in subject s/Distirbute/Distribute/.

Thanks,
Naoya Horiguchi

> ---
>  arch/x86/kernel/cpu/mcheck/mce.c |   18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 68317c8..966a5f5 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -785,13 +785,6 @@ static void mce_reign(void)
>  	 */
>  	if (global_worst <= MCE_KEEP_SEVERITY && mca_cfg.tolerant < 3)
>  		mce_panic("Machine check from unknown source", NULL, NULL);
> -
> -	/*
> -	 * Now clear all the mces_seen so that they don't reappear on
> -	 * the next mce.
> -	 */
> -	for_each_possible_cpu(cpu)
> -		memset(&per_cpu(mces_seen, cpu), 0, sizeof(struct mce));
>  }
>  
>  static atomic_t global_nwo;
> @@ -1137,9 +1130,6 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  		}
>  	}
>  
> -	/* mce_clear_state will clear *final, save locally for use later */
> -	m = *final;
> -
>  	if (!no_way_out)
>  		mce_clear_state(toclear);
>  
> @@ -1161,7 +1151,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  			mce_panic("Fatal machine check on current CPU", &m, msg);
>  		if (worst == MCE_AR_SEVERITY) {
>  			/* schedule action before return to userland */
> -			mce_save_info(m.addr, m.mcgstatus & MCG_STATUS_RIPV);
> +			mce_save_info(final->addr, final->mcgstatus & MCG_STATUS_RIPV);
>  			set_thread_flag(TIF_MCE_NOTIFY);
>  		} else if (kill_it) {
>  			force_sig(SIGBUS, current);
> @@ -1170,6 +1160,12 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  
>  	if (worst > 0)
>  		mce_report_event(regs);
> +
> +	/*
> +	 * Now clear the mces_seen of current CPU -*final - so that it does not
> +	 * reappear on the next mce.
> +	 */
> +	memset(final, 0, sizeof(struct mce));
>  	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
>  out:
>  	atomic_dec(&mce_entry);
> -- 
> 1.7.10.4
> 
> 
> 
> 

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