Re: [PATCH 2/3] x86, MCE: Drop default decoding notifier

[Prarit Bhargava <prarit@redhat.com>]

On 04/13/2011 09:36 AM, Borislav Petkov wrote:
> From: Borislav Petkov <borislav.petkov@amd.com>
> 
> The default notifier doesn't make a lot of sense to call in the
> correctable errors case. Drop it and emit the mcelog decoding hint only
> in the uncorrectable errors case and when no notifier is registered.
> 
> Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
> ---
>  arch/x86/include/asm/mce.h       |    4 ++--
>  arch/x86/kernel/cpu/mcheck/mce.c |   26 +++++++++-----------------
>  2 files changed, 11 insertions(+), 19 deletions(-)
> 
  
> +extern atomic_t mce_decoders;
> +

Boris,

I don't think we need to do this.  I think we can use the existing notifier chain tools to do this check for us ... *untested and uncompiled* patch below.

  	 * Print out human-readable details about the MCE error,
>  	 * (if the CPU has an implementation for that)
>  	 */
> -	atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
> +	if (!atomic_read(&mce_decoders)) {
> +		pr_emerg(HW_ERR "No human readable MCE decoding support on this CPU type.\n");
> +		pr_emerg(HW_ERR "Run the above through 'mcelog --ascii' to decode.\n");

I thought we didn't want these lines at all for CE errors?

> +	} else
> +		atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
>  }
>  
>  #define PANIC_TIMEOUT 5 /* 5 seconds */
> @@ -589,7 +582,8 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
>  		 */
>  		if (!(flags & MCP_DONTLOG) && !mce_dont_log_ce) {
>  			mce_log(&m);
> -			atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, &m);
> +			if (atomic_read(&mce_decoders))
> +				atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, &m);
>  		}
>  
>  		/*
> @@ -1721,8 +1715,6 @@ __setup("mce", mcheck_enable);
>  
>  int __init mcheck_init(void)
>  {
> -	atomic_notifier_chain_register(&x86_mce_decoder_chain, &mce_dec_nb);
> -
>  	mcheck_intel_therm_init();
>  
>  	return 0;

Again, this patch has not been tested or compiled against latest upstream.  I
have quickly tested it against RHEL6 (2.6.32,33,34,35,36,38,39 based) and
confirmed that I don't see the messages for CEs.  I have NOT fully tested to see what happens when I add in a "dummy" notifier to see if the messages are not printed.

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 3385ea2..b10a1f4 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -100,25 +100,12 @@ static int			cpu_missing;
 
 /*
  * CPU/chipset specific EDAC code can register a notifier call here to print
- * MCE errors in a human-readable form.
+ * MCE errors in a human-readable form.  Notifiers must return NOTIFY_STOP
+ * upon completion.
  */
 ATOMIC_NOTIFIER_HEAD(x86_mce_decoder_chain);
 EXPORT_SYMBOL_GPL(x86_mce_decoder_chain);
 
-static int default_decode_mce(struct notifier_block *nb, unsigned long val,
-			       void *data)
-{
-	pr_emerg(HW_ERR "No human readable MCE decoding support on this CPU type.\n");
-	pr_emerg(HW_ERR "Run the message through 'mcelog --ascii' to decode.\n");
-
-	return NOTIFY_STOP;
-}
-
-static struct notifier_block mce_dec_nb = {
-	.notifier_call = default_decode_mce,
-	.priority      = -1,
-};
-
 /* MCA banks polled by the period polling timer for corrected events */
 DEFINE_PER_CPU(mce_banks_t, mce_poll_banks) = {
 	[0 ... BITS_TO_LONGS(MAX_NR_BANKS)-1] = ~0UL
@@ -212,6 +199,8 @@ void mce_log(struct mce *mce)
 
 static void print_mce(struct mce *m)
 {
+	int ret;
+
 	pr_emerg(HW_ERR "CPU %d: Machine Check Exception: %Lx Bank %d: %016Lx\n",
 	       m->extcpu, m->mcgstatus, m->bank, m->status);
 
@@ -236,10 +225,13 @@ static void print_mce(struct mce *m)
 		m->cpuvendor, m->cpuid, m->time, m->socketid, m->apicid);
 
 	/*
-	 * Print out human-readable details about the MCE error,
-	 * (if the CPU has an implementation for that)
+	 * Output a message if the CPU has human-readable information for
+	 * unhandled UC errors
 	 */
-	atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
+	ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, &m);
+	if ((ret != NOTIFY_STOP) && (m->status & MCI_STATUS_UC))
+		pr_emerg(HW_ERR "Run the message through 'mcelog --ascii' "
+			 "to decode.\n");
 }
 
 #define PANIC_TIMEOUT 5 /* 5 seconds */
@@ -589,8 +581,8 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
 		 */
 		if (!(flags & MCP_DONTLOG) && !mce_dont_log_ce) {
 			mce_log(&m);
-			atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, &m);
-			add_taint(TAINT_MACHINE_CHECK);
+			atomic_notifier_call_chain(&x86_mce_decoder_chain, 0,
+						   &m);
 		}
 
 		/*
@@ -1722,8 +1714,6 @@ __setup("mce", mcheck_enable);
 
 int __init mcheck_init(void)
 {
-	atomic_notifier_chain_register(&x86_mce_decoder_chain, &mce_dec_nb);
-
 	mcheck_intel_therm_init();
 
 	return 0;