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authorPaul E. McKenney <paulmck@kernel.org>2022-12-16 16:52:01 -0800
committerPaul E. McKenney <paulmck@kernel.org>2023-01-19 15:55:12 -0800
commit344da544f177f919cf6919e5abcd388f27aa53db (patch)
tree47fbf9344fd33a71023a235f45e219be672e421a /arch/x86
parent1a3ea611fc105759cf1023e922d00cf44569b8bb (diff)
x86/nmi: Print reasons why backtrace NMIs are ignored
Instrument nmi_trigger_cpumask_backtrace() to dump out diagnostics based on evidence accumulated by exc_nmi(). These diagnostics are dumped for CPUs that ignored an NMI backtrace request for more than 10 seconds. [ paulmck: Apply Ingo Molnar feedback. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: <x86@kernel.org> Reviewed-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kernel/nmi.c73
1 files changed, 73 insertions, 0 deletions
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 701ff27a77ec..c315b18ec7c8 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -570,6 +570,79 @@ DEFINE_IDTENTRY_RAW(exc_nmi_noist)
EXPORT_SYMBOL_GPL(asm_exc_nmi_noist);
#endif
+#ifdef CONFIG_NMI_CHECK_CPU
+
+static char *nmi_check_stall_msg[] = {
+/* */
+/* +--------- nsp->idt_seq_snap & 0x1: CPU is in NMI handler. */
+/* | +------ cpu_is_offline(cpu) */
+/* | | +--- nsp->idt_calls_snap != atomic_long_read(&nsp->idt_calls): */
+/* | | | NMI handler has been invoked. */
+/* | | | */
+/* V V V */
+/* 0 0 0 */ "NMIs are not reaching exc_nmi() handler",
+/* 0 0 1 */ "exc_nmi() handler is ignoring NMIs",
+/* 0 1 0 */ "CPU is offline and NMIs are not reaching exc_nmi() handler",
+/* 0 1 1 */ "CPU is offline and exc_nmi() handler is legitimately ignoring NMIs",
+/* 1 0 0 */ "CPU is in exc_nmi() handler and no further NMIs are reaching handler",
+/* 1 0 1 */ "CPU is in exc_nmi() handler which is legitimately ignoring NMIs",
+/* 1 1 0 */ "CPU is offline in exc_nmi() handler and no more NMIs are reaching exc_nmi() handler",
+/* 1 1 1 */ "CPU is offline in exc_nmi() handler which is legitimately ignoring NMIs",
+};
+
+void nmi_backtrace_stall_snap(const struct cpumask *btp)
+{
+ int cpu;
+ struct nmi_stats *nsp;
+
+ for_each_cpu(cpu, btp) {
+ nsp = per_cpu_ptr(&nmi_stats, cpu);
+ nsp->idt_seq_snap = READ_ONCE(nsp->idt_seq);
+ nsp->idt_nmi_seq_snap = READ_ONCE(nsp->idt_nmi_seq);
+ nsp->idt_ignored_snap = READ_ONCE(nsp->idt_ignored);
+ nsp->idt_calls_snap = atomic_long_read(&nsp->idt_calls);
+ }
+}
+
+void nmi_backtrace_stall_check(const struct cpumask *btp)
+{
+ int cpu;
+ int idx;
+ unsigned long nmi_seq;
+ unsigned long j = jiffies;
+ char *modp;
+ char *msgp;
+ char *msghp;
+ struct nmi_stats *nsp;
+
+ for_each_cpu(cpu, btp) {
+ nsp = per_cpu_ptr(&nmi_stats, cpu);
+ modp = "";
+ msghp = "";
+ nmi_seq = READ_ONCE(nsp->idt_nmi_seq);
+ if (nsp->idt_nmi_seq_snap + 1 == nmi_seq && (nmi_seq & 0x1)) {
+ msgp = "CPU entered NMI handler function, but has not exited";
+ } else if ((nsp->idt_nmi_seq_snap & 0x1) != (nmi_seq & 0x1)) {
+ msgp = "CPU is handling NMIs";
+ } else {
+ idx = ((nsp->idt_seq_snap & 0x1) << 2) |
+ (cpu_is_offline(cpu) << 1) |
+ (nsp->idt_calls_snap != atomic_long_read(&nsp->idt_calls));
+ msgp = nmi_check_stall_msg[idx];
+ if (nsp->idt_ignored_snap != READ_ONCE(nsp->idt_ignored) && (idx & 0x1))
+ modp = ", but OK because ignore_nmis was set";
+ if (nmi_seq & ~0x1)
+ msghp = " (CPU currently in NMI handler function)";
+ else if (nsp->idt_nmi_seq_snap + 1 == nmi_seq)
+ msghp = " (CPU exited one NMI handler function)";
+ }
+ pr_alert("%s: CPU %d: %s%s%s, last activity: %lu jiffies ago.\n",
+ __func__, cpu, msgp, modp, msghp, j - READ_ONCE(nsp->recv_jiffies));
+ }
+}
+
+#endif
+
void stop_nmi(void)
{
ignore_nmis++;