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authorAaron Tomlin <atomlin@redhat.com>2014-06-23 13:22:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-23 16:47:44 -0700
commited235875e2ca983197831337a986f0517074e1a0 (patch)
treea562c7ac13452a0573b87977df7b26a6471ece38 /kernel
parentf3aca3d09525f87731ba6b892c9b010570bc54b4 (diff)
kernel/watchdog.c: print traces for all cpus on lockup detection
A 'softlockup' is defined as a bug that causes the kernel to loop in kernel mode for more than a predefined period to time, without giving other tasks a chance to run. Currently, upon detection of this condition by the per-cpu watchdog task, debug information (including a stack trace) is sent to the system log. On some occasions, we have observed that the "victim" rather than the actual "culprit" (i.e. the owner/holder of the contended resource) is reported to the user. Often this information has proven to be insufficient to assist debugging efforts. To avoid loss of useful debug information, for architectures which support NMI, this patch makes it possible to improve soft lockup reporting. This is accomplished by issuing an NMI to each cpu to obtain a stack trace. If NMI is not supported we just revert back to the old method. A sysctl and boot-time parameter is available to toggle this feature. [dzickus@redhat.com: add CONFIG_SMP in certain areas] [akpm@linux-foundation.org: additional CONFIG_SMP=n optimisations] [mq@suse.cz: fix warning] Signed-off-by: Aaron Tomlin <atomlin@redhat.com> Signed-off-by: Don Zickus <dzickus@redhat.com> Cc: David S. Miller <davem@davemloft.net> Cc: Mateusz Guzik <mguzik@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Jan Moskyto Matejka <mq@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sysctl.c11
-rw-r--r--kernel/watchdog.c39
2 files changed, 50 insertions, 0 deletions
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 075d1903138..75b22e22a72 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -860,6 +860,17 @@ static struct ctl_table kern_table[] = {
.extra1 = &zero,
.extra2 = &one,
},
+#ifdef CONFIG_SMP
+ {
+ .procname = "softlockup_all_cpu_backtrace",
+ .data = &sysctl_softlockup_all_cpu_backtrace,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
+#endif /* CONFIG_SMP */
{
.procname = "nmi_watchdog",
.data = &watchdog_user_enabled,
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 30e482240da..c3319bd1b04 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -31,6 +31,12 @@
int watchdog_user_enabled = 1;
int __read_mostly watchdog_thresh = 10;
+#ifdef CONFIG_SMP
+int __read_mostly sysctl_softlockup_all_cpu_backtrace;
+#else
+#define sysctl_softlockup_all_cpu_backtrace 0
+#endif
+
static int __read_mostly watchdog_running;
static u64 __read_mostly sample_period;
@@ -47,6 +53,7 @@ static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
#endif
+static unsigned long soft_lockup_nmi_warn;
/* boot commands */
/*
@@ -95,6 +102,15 @@ static int __init nosoftlockup_setup(char *str)
}
__setup("nosoftlockup", nosoftlockup_setup);
/* */
+#ifdef CONFIG_SMP
+static int __init softlockup_all_cpu_backtrace_setup(char *str)
+{
+ sysctl_softlockup_all_cpu_backtrace =
+ !!simple_strtol(str, NULL, 0);
+ return 1;
+}
+__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
+#endif
/*
* Hard-lockup warnings should be triggered after just a few seconds. Soft-
@@ -271,6 +287,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
struct pt_regs *regs = get_irq_regs();
int duration;
+ int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
/* kick the hardlockup detector */
watchdog_interrupt_count();
@@ -317,6 +334,17 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
if (__this_cpu_read(soft_watchdog_warn) == true)
return HRTIMER_RESTART;
+ if (softlockup_all_cpu_backtrace) {
+ /* Prevent multiple soft-lockup reports if one cpu is already
+ * engaged in dumping cpu back traces
+ */
+ if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
+ /* Someone else will report us. Let's give up */
+ __this_cpu_write(soft_watchdog_warn, true);
+ return HRTIMER_RESTART;
+ }
+ }
+
printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
smp_processor_id(), duration,
current->comm, task_pid_nr(current));
@@ -327,6 +355,17 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
else
dump_stack();
+ if (softlockup_all_cpu_backtrace) {
+ /* Avoid generating two back traces for current
+ * given that one is already made above
+ */
+ trigger_allbutself_cpu_backtrace();
+
+ clear_bit(0, &soft_lockup_nmi_warn);
+ /* Barrier to sync with other cpus */
+ smp_mb__after_atomic();
+ }
+
if (softlockup_panic)
panic("softlockup: hung tasks");
__this_cpu_write(soft_watchdog_warn, true);