From e31d6883f21c1cdfe5bc64e28411f8a92b783fde Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 3 Oct 2017 16:37:53 +0200 Subject: [PATCH] watchdog/core, powerpc: Lock cpus across reconfiguration Instead of dropping the cpu hotplug lock after stopping NMI watchdog and threads and reaquiring for restart, the code and the protection rules become more obvious when holding cpu hotplug lock across the full reconfiguration. Suggested-by: Linus Torvalds Signed-off-by: Thomas Gleixner Acked-by: Michael Ellerman Cc: Peter Zijlstra Cc: Don Zickus Cc: Benjamin Herrenschmidt Cc: Nicholas Piggin Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1710022105570.2114@nanos --- arch/powerpc/kernel/watchdog.c | 4 ---- kernel/smpboot.c | 3 +-- kernel/watchdog.c | 10 +++++++++- 3 files changed, 10 insertions(+), 7 deletions(-) diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c index 2673ec8bec00..f9b4c6352d24 100644 --- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -359,21 +359,17 @@ void watchdog_nmi_stop(void) { int cpu; - cpus_read_lock(); for_each_cpu(cpu, &wd_cpus_enabled) stop_wd_on_cpu(cpu); - cpus_read_unlock(); } void watchdog_nmi_start(void) { int cpu; - cpus_read_lock(); watchdog_calc_timeouts(); for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) start_wd_on_cpu(cpu); - cpus_read_unlock(); } /* diff --git a/kernel/smpboot.c b/kernel/smpboot.c index ed7507b69b48..5043e7433f4b 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -351,7 +351,7 @@ void smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread static struct cpumask tmp; unsigned int cpu; - get_online_cpus(); + lockdep_assert_cpus_held(); mutex_lock(&smpboot_threads_lock); /* Park threads that were exclusively enabled on the old mask. */ @@ -367,7 +367,6 @@ void smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread cpumask_copy(old, new); mutex_unlock(&smpboot_threads_lock); - put_online_cpus(); } static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD); diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 6ad6226535d0..fff90fe10007 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -535,7 +535,6 @@ static void softlockup_update_smpboot_threads(void) smpboot_update_cpumask_percpu_thread(&watchdog_threads, &watchdog_allowed_mask); - __lockup_detector_cleanup(); } /* Temporarily park all watchdog threads */ @@ -554,6 +553,7 @@ static void softlockup_unpark_threads(void) static void softlockup_reconfigure_threads(void) { + cpus_read_lock(); watchdog_nmi_stop(); softlockup_park_all_threads(); set_sample_period(); @@ -561,6 +561,12 @@ static void softlockup_reconfigure_threads(void) if (watchdog_enabled && watchdog_thresh) softlockup_unpark_threads(); watchdog_nmi_start(); + cpus_read_unlock(); + /* + * Must be called outside the cpus locked section to prevent + * recursive locking in the perf code. + */ + __lockup_detector_cleanup(); } /* @@ -605,9 +611,11 @@ static inline void watchdog_disable_all_cpus(void) { } static inline void softlockup_init_threads(void) { } static void softlockup_reconfigure_threads(void) { + cpus_read_lock(); watchdog_nmi_stop(); lockup_detector_update_enable(); watchdog_nmi_start(); + cpus_read_unlock(); } #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */