5 files changed, 73 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 884904975d0b..c1b9aa8c5a52 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3130,6 +3130,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         [KNL] Should the soft-lockup detector generate panics.
                         Format: <integer>
 
+        softlockup_all_cpu_backtrace=
+                        [KNL] Should the soft-lockup detector generate
+                        backtraces on all cpus.
+                        Format: <integer>
+
         sonypi.*=       [HW] Sony Programmable I/O Control Device driver
                         See Documentation/laptops/sonypi.txt
 
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 708bb7f1b7e0..c14374e71775 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -75,6 +75,7 @@ show up in /proc/sys/kernel:
 - shmall
 - shmmax                      [ sysv ipc ]
 - shmmni
+- softlockup_all_cpu_backtrace
 - stop-a                      [ SPARC only ]
 - sysrq                       ==> Documentation/sysrq.txt
 - sysctl_writes_strict
@@ -783,6 +784,22 @@ via the /proc/sys interface:
 
 ==============================================================
 
+softlockup_all_cpu_backtrace:
+
+This value controls the soft lockup detector thread's behavior
+when a soft lockup condition is detected as to whether or not
+to gather further debug information. If enabled, each cpu will
+be issued an NMI and instructed to capture stack trace.
+
+This feature is only applicable for architectures which support
+NMI.
+
+0: do nothing. This is the default behavior.
+
+1: on detection capture more debug information.
+
+==============================================================
+
 tainted:
 
 Non-zero if the kernel has been tainted.  Numeric values, which
diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index a17ab6398d7c..447775ee2c4b 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -57,6 +57,7 @@ int hw_nmi_is_cpu_stuck(struct pt_regs *);
 u64 hw_nmi_get_sample_period(int watchdog_thresh);
 extern int watchdog_user_enabled;
 extern int watchdog_thresh;
+extern int sysctl_softlockup_all_cpu_backtrace;
 struct ctl_table;
 extern int proc_dowatchdog(struct ctl_table *, int ,
                            void __user *, size_t *, loff_t *);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 075d1903138f..75b22e22a72c 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 30e482240dae..c3319bd1b040 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);