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Commit 6e7458a6 authored by Ulrich Obergfell's avatar Ulrich Obergfell Committed by Linus Torvalds
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kernel/watchdog.c: control hard lockup detection default 



In some cases we don't want hard lockup detection enabled by default.
An example is when running as a guest.  Introduce

  watchdog_enable_hardlockup_detector(bool)

allowing those cases to disable hard lockup detection.  This must be
executed early by the boot processor from e.g.  smp_prepare_boot_cpu, in
order to allow kernel command line arguments to override it, as well as
to avoid hard lockup detection being enabled before we've had a chance
to indicate that it's unwanted.  In summary,

  initial boot:					default=enabled
  smp_prepare_boot_cpu
    watchdog_enable_hardlockup_detector(false):	default=disabled
  cmdline has 'nmi_watchdog=1':			default=enabled

The running kernel still has the ability to enable/disable at any time
with /proc/sys/kernel/nmi_watchdog us usual.  However even when the
default has been overridden /proc/sys/kernel/nmi_watchdog will initially
show '1'.  To truly turn it on one must disable/enable it, i.e.

  echo 0 > /proc/sys/kernel/nmi_watchdog
  echo 1 > /proc/sys/kernel/nmi_watchdog

This patch will be immediately useful for KVM with the next patch of this
series.  Other hypervisor guest types may find it useful as well.

[akpm@linux-foundation.org: fix build]
[dzickus@redhat.com: fix compile issues on sparc]
Signed-off-by: default avatarUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: default avatarAndrew Jones <drjones@redhat.com>
Signed-off-by: default avatarDon Zickus <dzickus@redhat.com>
Signed-off-by: default avatarDon Zickus <dzickus@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8a1db928

include/linux/nmi.h

+13 −0
Original line number Diff line number Diff line
@@ -24,6 +24,19 @@ static inline void touch_nmi_watchdog(void) 
}

#endif



#if defined(CONFIG_HARDLOCKUP_DETECTOR)

extern void watchdog_enable_hardlockup_detector(bool val);

extern bool watchdog_hardlockup_detector_is_enabled(void);

#else

static inline void watchdog_enable_hardlockup_detector(bool val)

{

}

static inline bool watchdog_hardlockup_detector_is_enabled(void)

{

	return true;

}

#endif



/*

 * Create trigger_all_cpu_backtrace() out of the arch-provided

 * base function. Return whether such support was available,

kernel/watchdog.c

+48 −2
Original line number Diff line number Diff line
@@ -59,6 +59,25 @@ static unsigned long soft_lockup_nmi_warn; 
static int hardlockup_panic =

			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;



static bool hardlockup_detector_enabled = true;

/*

 * 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

 * cases this function can be called to disable hard lockup detection. This

 * function should only be executed once by the boot processor before the

 * kernel command line parameters are parsed, because otherwise it is not

 * possible to override this in hardlockup_panic_setup().

 */

void watchdog_enable_hardlockup_detector(bool val)

{

	hardlockup_detector_enabled = val;

}



bool watchdog_hardlockup_detector_is_enabled(void)

{

	return hardlockup_detector_enabled;

}



static int __init hardlockup_panic_setup(char *str)

{

	if (!strncmp(str, "panic", 5))
@@ -67,6 +86,14 @@ static int __init hardlockup_panic_setup(char *str) 
		hardlockup_panic = 0;

	else if (!strncmp(str, "0", 1))

		watchdog_user_enabled = 0;

	else if (!strncmp(str, "1", 1) || !strncmp(str, "2", 1)) {

		/*

		 * Setting 'nmi_watchdog=1' or 'nmi_watchdog=2' (legacy option)

		 * has the same effect.

		 */

		watchdog_user_enabled = 1;

		watchdog_enable_hardlockup_detector(true);

	}

	return 1;

}

__setup("nmi_watchdog=", hardlockup_panic_setup);
@@ -465,6 +492,15 @@ static int watchdog_nmi_enable(unsigned int cpu) 
	struct perf_event_attr *wd_attr;

	struct perf_event *event = per_cpu(watchdog_ev, cpu);



	/*

	 * Some kernels need to default hard lockup detection to

	 * 'disabled', for example a guest on a hypervisor.

	 */

	if (!watchdog_hardlockup_detector_is_enabled()) {

		event = ERR_PTR(-ENOENT);

		goto handle_err;

	}



	/* is it already setup and enabled? */

	if (event && event->state > PERF_EVENT_STATE_OFF)

		goto out;
@@ -479,6 +515,7 @@ static int watchdog_nmi_enable(unsigned int cpu) 
	/* Try to register using hardware perf events */

	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);



handle_err:

	/* save cpu0 error for future comparision */

	if (cpu == 0 && IS_ERR(event))

		cpu0_err = PTR_ERR(event);
@@ -624,11 +661,13 @@ int proc_dowatchdog(struct ctl_table *table, int write, 
		    void __user *buffer, size_t *lenp, loff_t *ppos)

{

	int err, old_thresh, old_enabled;

	bool old_hardlockup;

	static DEFINE_MUTEX(watchdog_proc_mutex);



	mutex_lock(&watchdog_proc_mutex);

	old_thresh = ACCESS_ONCE(watchdog_thresh);

	old_enabled = ACCESS_ONCE(watchdog_user_enabled);

	old_hardlockup = watchdog_hardlockup_detector_is_enabled();



	err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

	if (err || !write)
@@ -640,15 +679,22 @@ int proc_dowatchdog(struct ctl_table *table, int write, 
	 * disabled. The 'watchdog_running' variable check in

	 * watchdog_*_all_cpus() function takes care of this.

	 */

	if (watchdog_user_enabled && watchdog_thresh)

	if (watchdog_user_enabled && watchdog_thresh) {

		/*

		 * Prevent a change in watchdog_thresh accidentally overriding

		 * the enablement of the hardlockup detector.

		 */

		if (watchdog_user_enabled != old_enabled)

			watchdog_enable_hardlockup_detector(true);

		err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);

	else

	} else

		watchdog_disable_all_cpus();



	/* Restore old values on failure */

	if (err) {

		watchdog_thresh = old_thresh;

		watchdog_user_enabled = old_enabled;

		watchdog_enable_hardlockup_detector(old_hardlockup);

	}

out:

	mutex_unlock(&watchdog_proc_mutex);