On Wed, 23 Apr 2014 16:40:05 -0400 Don Zickus <dzickus@xxxxxxxxxx> wrote:
> From: Aaron Tomlin <atomlin@xxxxxxxxxx>
>
> 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.
>
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -57,6 +57,9 @@ 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;
> +#ifdef CONFIG_SMP
> +extern int sysctl_softlockup_all_cpu_backtrace;
> +#endif
The ifdefs aren't really needed here. If we omit them then error
reporting happens at link time rather than at compile time, but that's
a small price to pay for cleaning up the code.
> + 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;
> + }
> + }
You missed my suggestion here.
text data bss dec hex filename
1519 524 24 2067 813 kernel/watchdog.o-before
1471 520 16 2007 7d7 kernel/watchdog.o-after
--- a/include/linux/nmi.h~watchdog-printing-traces-for-all-cpus-on-lockup-detection-fix
+++ a/include/linux/nmi.h
@@ -57,9 +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;
-#ifdef CONFIG_SMP
extern int sysctl_softlockup_all_cpu_backtrace;
-#endif
struct ctl_table;
extern int proc_dowatchdog(struct ctl_table *, int ,
void __user *, size_t *, loff_t *);
--- a/kernel/watchdog.c~watchdog-printing-traces-for-all-cpus-on-lockup-detection-fix
+++ a/kernel/watchdog.c
@@ -31,7 +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;
_
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