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kernel/watchdog.c: control hard lockup detection default

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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: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ulrich Obergfell 2014-10-13 15:55:35 -07:00 committed by Linus Torvalds
parent 8a1db92830
commit 6e7458a6f0
2 changed files with 61 additions and 2 deletions
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13
include/linux/nmi.h
View file

@ -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,

50
kernel/watchdog.c
View file

@ -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);