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Date:   Fri, 08 Jan 2021 17:09:18 -0000
From:   "tip-bot2 for Paul E. McKenney" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jonathan Lemon <bsd@...com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Borislav Petkov <bp@...e.de>, Tony Luck <tony.luck@...el.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: ras/core] x86/mce: Make mce_timed_out() identify holdout CPUs

The following commit has been merged into the ras/core branch of tip:

Commit-ID:     7bb39313cd6239e7eb95198950a02b4ad2a08316
Gitweb:        https://git.kernel.org/tip/7bb39313cd6239e7eb95198950a02b4ad2a08316
Author:        Paul E. McKenney <paulmck@...nel.org>
AuthorDate:    Wed, 23 Dec 2020 17:04:19 -08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Fri, 08 Jan 2021 18:00:09 +01:00

x86/mce: Make mce_timed_out() identify holdout CPUs

The

  "Timeout: Not all CPUs entered broadcast exception handler"

message will appear from time to time given enough systems, but this
message does not identify which CPUs failed to enter the broadcast
exception handler. This information would be valuable if available,
for example, in order to correlate with other hardware-oriented error
messages.

Add a cpumask of CPUs which maintains which CPUs have entered this
handler, and print out which ones failed to enter in the event of a
timeout.

 [ bp: Massage. ]

Reported-by: Jonathan Lemon <bsd@...com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Tested-by: Tony Luck <tony.luck@...el.com>
Link: https://lkml.kernel.org/r/20210106174102.GA23874@paulmck-ThinkPad-P72
---
 arch/x86/kernel/cpu/mce/core.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 13d3f1c..6c81d09 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -878,6 +878,12 @@ static atomic_t mce_executing;
 static atomic_t mce_callin;
 
 /*
+ * Track which CPUs entered the MCA broadcast synchronization and which not in
+ * order to print holdouts.
+ */
+static cpumask_t mce_missing_cpus = CPU_MASK_ALL;
+
+/*
  * Check if a timeout waiting for other CPUs happened.
  */
 static int mce_timed_out(u64 *t, const char *msg)
@@ -894,8 +900,12 @@ static int mce_timed_out(u64 *t, const char *msg)
 	if (!mca_cfg.monarch_timeout)
 		goto out;
 	if ((s64)*t < SPINUNIT) {
-		if (mca_cfg.tolerant <= 1)
+		if (mca_cfg.tolerant <= 1) {
+			if (cpumask_and(&mce_missing_cpus, cpu_online_mask, &mce_missing_cpus))
+				pr_emerg("CPUs not responding to MCE broadcast (may include false positives): %*pbl\n",
+					 cpumask_pr_args(&mce_missing_cpus));
 			mce_panic(msg, NULL, NULL);
+		}
 		cpu_missing = 1;
 		return 1;
 	}
@@ -1006,6 +1016,7 @@ static int mce_start(int *no_way_out)
 	 * is updated before mce_callin.
 	 */
 	order = atomic_inc_return(&mce_callin);
+	cpumask_clear_cpu(smp_processor_id(), &mce_missing_cpus);
 
 	/*
 	 * Wait for everyone.
@@ -1114,6 +1125,7 @@ static int mce_end(int order)
 reset:
 	atomic_set(&global_nwo, 0);
 	atomic_set(&mce_callin, 0);
+	cpumask_setall(&mce_missing_cpus);
 	barrier();
 
 	/*
@@ -2712,6 +2724,7 @@ static void mce_reset(void)
 	atomic_set(&mce_executing, 0);
 	atomic_set(&mce_callin, 0);
 	atomic_set(&global_nwo, 0);
+	cpumask_setall(&mce_missing_cpus);
 }
 
 static int fake_panic_get(void *data, u64 *val)

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