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watchdog/hardlockup/perf: Prevent CPU hotplug deadlock

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The following deadlock is possible in the watchdog hotplug code:

  cpus_write_lock()
    ...
      takedown_cpu()
        smpboot_park_threads()
          smpboot_park_thread()
            kthread_park()
              ->park() := watchdog_disable()
                watchdog_nmi_disable()
                  perf_event_release_kernel();
                    put_event()
                      _free_event()
                        ->destroy() := hw_perf_event_destroy()
                          x86_release_hardware()
                            release_ds_buffers()
                              get_online_cpus()

when a per cpu watchdog perf event is destroyed which drops the last
reference to the PMU hardware. The cleanup code there invokes
get_online_cpus() which instantly deadlocks because the hotplug percpu
rwsem is write locked.

To solve this add a deferring mechanism:

  cpus_write_lock()
			   kthread_park()
			    watchdog_nmi_disable(deferred)
			      perf_event_disable(event);
			      move_event_to_deferred(event);
			   ....
  cpus_write_unlock()
  cleaup_deferred_events()
    perf_event_release_kernel()

This is still properly serialized against concurrent hotplug via the
cpu_add_remove_lock, which is held by the task which initiated the hotplug
event.

This is also used to handle event destruction when the watchdog threads are
parked via other mechanisms than CPU hotplug.

Analyzed-by: Peter Zijlstra <peterz@infradead.org>

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194146.884469246@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Thomas Gleixner
2017-09-12 21:37:04 +02:00
committed by Ingo Molnar
parent 20d853fd07
commit 941154bd69
4 changed files with 65 additions and 6 deletions
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6
include/linux/nmi.h
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@@ -13,9 +13,11 @@
#ifdef CONFIG_LOCKUP_DETECTOR
void lockup_detector_init(void);
void lockup_detector_soft_poweroff(void);
void lockup_detector_cleanup(void);
#else
static inline void lockup_detector_init(void) { }
static inline void lockup_detector_soft_poweroff(void) { }
static inline void lockup_detector_cleanup(void) { }
#endif
#ifdef CONFIG_SOFTLOCKUP_DETECTOR
@@ -77,9 +79,13 @@ static inline void hardlockup_detector_disable(void) {}
extern void arch_touch_nmi_watchdog(void);
extern void hardlockup_detector_perf_stop(void);
extern void hardlockup_detector_perf_restart(void);
extern void hardlockup_detector_perf_disable(void);
extern void hardlockup_detector_perf_cleanup(void);
#else
static inline void hardlockup_detector_perf_stop(void) { }
static inline void hardlockup_detector_perf_restart(void) { }
static inline void hardlockup_detector_perf_disable(void) { }
static inline void hardlockup_detector_perf_cleanup(void) { }
#if !defined(CONFIG_HAVE_NMI_WATCHDOG)
static inline void arch_touch_nmi_watchdog(void) {}
#endif