kernel/watchdog.c: perform all-CPU backtrace in case of hard lockup
In many cases of hardlockup reports, it's actually not possible to know
why it triggered, because the CPU that got stuck is usually waiting on a
resource (with IRQs disabled) in posession of some other CPU is holding.
IOW, we are often looking at the stacktrace of the victim and not the
actual offender.
Introduce sysctl / cmdline parameter that makes it possible to have
hardlockup detector perform all-CPU backtrace.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 6263a2d..0231f45 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1269,6 +1269,11 @@
Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
Default: 1024
+ hardlockup_all_cpu_backtrace=
+ [KNL] Should the hard-lockup detector generate
+ backtraces on all cpus.
+ Format: <integer>
+
hashdist= [KNL,NUMA] Large hashes allocated during boot
are distributed across NUMA nodes. Defaults on
for 64-bit NUMA, off otherwise.
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 6fccb69..af70d15 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -33,6 +33,7 @@
- domainname
- hostname
- hotplug
+- hardlockup_all_cpu_backtrace
- hung_task_panic
- hung_task_check_count
- hung_task_timeout_secs
@@ -293,6 +294,17 @@
see the hostname(1) man page.
==============================================================
+hardlockup_all_cpu_backtrace:
+
+This value controls the hard lockup detector behavior when a hard
+lockup condition is detected as to whether or not to gather further
+debug information. If enabled, arch-specific all-CPU stack dumping
+will be initiated.
+
+0: do nothing. This is the default behavior.
+
+1: on detection capture more debug information.
+==============================================================
hotplug:
diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 78488e0..7ec5b86 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -73,6 +73,7 @@
extern int watchdog_thresh;
extern unsigned long *watchdog_cpumask_bits;
extern int sysctl_softlockup_all_cpu_backtrace;
+extern int sysctl_hardlockup_all_cpu_backtrace;
struct ctl_table;
extern int proc_watchdog(struct ctl_table *, int ,
void __user *, size_t *, loff_t *);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 96c856b..1a5faa3e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -898,6 +898,15 @@
.extra1 = &zero,
.extra2 = &one,
},
+ {
+ .procname = "hardlockup_all_cpu_backtrace",
+ .data = &sysctl_hardlockup_all_cpu_backtrace,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
#endif /* CONFIG_SMP */
#endif
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 452e4ed..f6b32b8 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -57,8 +57,10 @@
#ifdef CONFIG_SMP
int __read_mostly sysctl_softlockup_all_cpu_backtrace;
+int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
#else
#define sysctl_softlockup_all_cpu_backtrace 0
+#define sysctl_hardlockup_all_cpu_backtrace 0
#endif
static struct cpumask watchdog_cpumask __read_mostly;
unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
@@ -112,6 +114,7 @@
#ifdef CONFIG_HARDLOCKUP_DETECTOR
static int hardlockup_panic =
CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
+static unsigned long hardlockup_allcpu_dumped;
/*
* We may not want to enable hard lockup detection by default in all cases,
* for example when running the kernel as a guest on a hypervisor. In these
@@ -173,6 +176,13 @@
return 1;
}
__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
+static int __init hardlockup_all_cpu_backtrace_setup(char *str)
+{
+ sysctl_hardlockup_all_cpu_backtrace =
+ !!simple_strtol(str, NULL, 0);
+ return 1;
+}
+__setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
#endif
/*
@@ -318,17 +328,30 @@
*/
if (is_hardlockup()) {
int this_cpu = smp_processor_id();
+ struct pt_regs *regs = get_irq_regs();
/* only print hardlockups once */
if (__this_cpu_read(hard_watchdog_warn) == true)
return;
- if (hardlockup_panic)
- panic("Watchdog detected hard LOCKUP on cpu %d",
- this_cpu);
+ pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
+ print_modules();
+ print_irqtrace_events(current);
+ if (regs)
+ show_regs(regs);
else
- WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
- this_cpu);
+ dump_stack();
+
+ /*
+ * Perform all-CPU dump only once to avoid multiple hardlockups
+ * generating interleaving traces
+ */
+ if (sysctl_hardlockup_all_cpu_backtrace &&
+ !test_and_set_bit(0, &hardlockup_allcpu_dumped))
+ trigger_allbutself_cpu_backtrace();
+
+ if (hardlockup_panic)
+ panic("Hard LOCKUP");
__this_cpu_write(hard_watchdog_warn, true);
return;