Commit e18a5ebc authored by Linus Torvalds's avatar Linus Torvalds

Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull watchdog fix from Thomas Gleixner:
 "A fix for the hardlockup watchdog to prevent false positives with
  extreme Turbo-Modes which make the perf/NMI watchdog fire faster than
  the hrtimer which is used to verify.

  Slightly larger than the minimal fix, which just would increase the
  hrtimer frequency, but comes with extra overhead of more watchdog
  timer interrupts and thread wakeups for all users.

  With this change we restrict the overhead to the extreme Turbo-Mode
  systems"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  kernel/watchdog: Prevent false positives with turbo modes
parents 58d4e450 7edaeb68
...@@ -100,6 +100,7 @@ config X86 ...@@ -100,6 +100,7 @@ config X86
select GENERIC_STRNCPY_FROM_USER select GENERIC_STRNCPY_FROM_USER
select GENERIC_STRNLEN_USER select GENERIC_STRNLEN_USER
select GENERIC_TIME_VSYSCALL select GENERIC_TIME_VSYSCALL
select HARDLOCKUP_CHECK_TIMESTAMP if X86_64
select HAVE_ACPI_APEI if ACPI select HAVE_ACPI_APEI if ACPI
select HAVE_ACPI_APEI_NMI if ACPI select HAVE_ACPI_APEI_NMI if ACPI
select HAVE_ALIGNED_STRUCT_PAGE if SLUB select HAVE_ALIGNED_STRUCT_PAGE if SLUB
......
...@@ -168,6 +168,14 @@ extern int sysctl_hardlockup_all_cpu_backtrace; ...@@ -168,6 +168,14 @@ extern int sysctl_hardlockup_all_cpu_backtrace;
#define sysctl_softlockup_all_cpu_backtrace 0 #define sysctl_softlockup_all_cpu_backtrace 0
#define sysctl_hardlockup_all_cpu_backtrace 0 #define sysctl_hardlockup_all_cpu_backtrace 0
#endif #endif
#if defined(CONFIG_HARDLOCKUP_CHECK_TIMESTAMP) && \
defined(CONFIG_HARDLOCKUP_DETECTOR)
void watchdog_update_hrtimer_threshold(u64 period);
#else
static inline void watchdog_update_hrtimer_threshold(u64 period) { }
#endif
extern bool is_hardlockup(void); extern bool is_hardlockup(void);
struct ctl_table; struct ctl_table;
extern int proc_watchdog(struct ctl_table *, int , extern int proc_watchdog(struct ctl_table *, int ,
......
...@@ -240,6 +240,7 @@ static void set_sample_period(void) ...@@ -240,6 +240,7 @@ static void set_sample_period(void)
* hardlockup detector generates a warning * hardlockup detector generates a warning
*/ */
sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5); sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
watchdog_update_hrtimer_threshold(sample_period);
} }
/* Commands for resetting the watchdog */ /* Commands for resetting the watchdog */
......
...@@ -37,6 +37,62 @@ void arch_touch_nmi_watchdog(void) ...@@ -37,6 +37,62 @@ void arch_touch_nmi_watchdog(void)
} }
EXPORT_SYMBOL(arch_touch_nmi_watchdog); EXPORT_SYMBOL(arch_touch_nmi_watchdog);
#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
static DEFINE_PER_CPU(ktime_t, last_timestamp);
static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
void watchdog_update_hrtimer_threshold(u64 period)
{
/*
* The hrtimer runs with a period of (watchdog_threshold * 2) / 5
*
* So it runs effectively with 2.5 times the rate of the NMI
* watchdog. That means the hrtimer should fire 2-3 times before
* the NMI watchdog expires. The NMI watchdog on x86 is based on
* unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
* might run way faster than expected and the NMI fires in a
* smaller period than the one deduced from the nominal CPU
* frequency. Depending on the Turbo-Mode factor this might be fast
* enough to get the NMI period smaller than the hrtimer watchdog
* period and trigger false positives.
*
* The sample threshold is used to check in the NMI handler whether
* the minimum time between two NMI samples has elapsed. That
* prevents false positives.
*
* Set this to 4/5 of the actual watchdog threshold period so the
* hrtimer is guaranteed to fire at least once within the real
* watchdog threshold.
*/
watchdog_hrtimer_sample_threshold = period * 2;
}
static bool watchdog_check_timestamp(void)
{
ktime_t delta, now = ktime_get_mono_fast_ns();
delta = now - __this_cpu_read(last_timestamp);
if (delta < watchdog_hrtimer_sample_threshold) {
/*
* If ktime is jiffies based, a stalled timer would prevent
* jiffies from being incremented and the filter would look
* at a stale timestamp and never trigger.
*/
if (__this_cpu_inc_return(nmi_rearmed) < 10)
return false;
}
__this_cpu_write(nmi_rearmed, 0);
__this_cpu_write(last_timestamp, now);
return true;
}
#else
static inline bool watchdog_check_timestamp(void)
{
return true;
}
#endif
static struct perf_event_attr wd_hw_attr = { static struct perf_event_attr wd_hw_attr = {
.type = PERF_TYPE_HARDWARE, .type = PERF_TYPE_HARDWARE,
.config = PERF_COUNT_HW_CPU_CYCLES, .config = PERF_COUNT_HW_CPU_CYCLES,
...@@ -61,6 +117,9 @@ static void watchdog_overflow_callback(struct perf_event *event, ...@@ -61,6 +117,9 @@ static void watchdog_overflow_callback(struct perf_event *event,
return; return;
} }
if (!watchdog_check_timestamp())
return;
/* check for a hardlockup /* check for a hardlockup
* This is done by making sure our timer interrupt * This is done by making sure our timer interrupt
* is incrementing. The timer interrupt should have * is incrementing. The timer interrupt should have
......
...@@ -797,6 +797,13 @@ config HARDLOCKUP_DETECTOR_PERF ...@@ -797,6 +797,13 @@ config HARDLOCKUP_DETECTOR_PERF
bool bool
select SOFTLOCKUP_DETECTOR select SOFTLOCKUP_DETECTOR
#
# Enables a timestamp based low pass filter to compensate for perf based
# hard lockup detection which runs too fast due to turbo modes.
#
config HARDLOCKUP_CHECK_TIMESTAMP
bool
# #
# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard # arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard
# lockup detector rather than the perf based detector. # lockup detector rather than the perf based detector.
......
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