[PATCH 1/2] x86/mce: Rate-limit the CMCI storm transition notices

[Breno Leitao <leitao@debian.org>]

mce_track_storm() prints a line every time a bank enters storm mode and
another every time it leaves. Neither is bounded, so the log volume
follows whatever rate the bank flaps at.

One host in our fleet logged 9970726 "CMCI storm detected" and 9970734
"CMCI storm subsided" lines for a single bank over four days, which is
a bit excessive for all monitoring purposes.

Put both transitions behind one ratelimit.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 arch/x86/kernel/cpu/mce/threshold.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/threshold.c b/arch/x86/kernel/cpu/mce/threshold.c
index 6c370d5af5bd2..8591715ce2430 100644
--- a/arch/x86/kernel/cpu/mce/threshold.c
+++ b/arch/x86/kernel/cpu/mce/threshold.c
@@ -4,6 +4,7 @@
  */
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
+#include <linux/ratelimit.h>
 
 #include <asm/irq_vectors.h>
 #include <asm/traps.h>
@@ -111,6 +112,13 @@ void cmci_storm_end(unsigned int bank)
 		mce_timer_kick(false);
 }
 
+/*
+ * Shared by both transitions so that a bank flapping between them cannot
+ * outrun the console.
+ */
+static DEFINE_RATELIMIT_STATE(storm_rs, DEFAULT_RATELIMIT_INTERVAL,
+			      DEFAULT_RATELIMIT_BURST);
+
 void mce_track_storm(struct mce *mce)
 {
 	struct mca_storm_desc *storm = this_cpu_ptr(&storm_desc);
@@ -150,13 +158,17 @@ void mce_track_storm(struct mce *mce)
 	if (storm->banks[mce->bank].in_storm_mode) {
 		if (history & GENMASK_ULL(STORM_END_POLL_THRESHOLD, 0))
 			return;
-		printk_deferred(KERN_NOTICE "CPU%d BANK%d CMCI storm subsided\n", smp_processor_id(), mce->bank);
+		if (__ratelimit(&storm_rs))
+			printk_deferred(KERN_NOTICE "CPU%d BANK%d CMCI storm subsided\n",
+					smp_processor_id(), mce->bank);
 		mce_handle_storm(mce->bank, false);
 		cmci_storm_end(mce->bank);
 	} else {
 		if (hweight64(history) < STORM_BEGIN_THRESHOLD)
 			return;
-		printk_deferred(KERN_NOTICE "CPU%d BANK%d CMCI storm detected\n", smp_processor_id(), mce->bank);
+		if (__ratelimit(&storm_rs))
+			printk_deferred(KERN_NOTICE "CPU%d BANK%d CMCI storm detected\n",
+					smp_processor_id(), mce->bank);
 		mce_handle_storm(mce->bank, true);
 		cmci_storm_begin(mce->bank);
 	}

-- 
2.53.0-Meta