From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Sebastian Siewior <bigeasy@linutronix.de>,
Paul McKenney <paulmck@linux.vnet.ibm.com>
Subject: [patch V3 29/32] cpu/hotplug: Convert hotplug locking to percpu rwsem
Date: Wed, 24 May 2017 10:15:40 +0200 [thread overview]
Message-ID: <20170524081549.447014063@linutronix.de> (raw)
In-Reply-To: 20170524081511.203800767@linutronix.de
[-- Attachment #1: cpuhotplug_Convert_hotplug_locking_to_percpu_rwsem.patch --]
[-- Type: text/plain, Size: 5531 bytes --]
There are no more (known) nested calls to get_online_cpus() and all
observed lock ordering problems have been addressed.
Replace the magic nested 'rwsem' hackery with a percpu-rwsem.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/cpu.h | 2
kernel/cpu.c | 107 ++++++----------------------------------------------
2 files changed, 14 insertions(+), 95 deletions(-)
Index: b/include/linux/cpu.h
===================================================================
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -103,7 +103,7 @@ extern void cpus_write_lock(void);
extern void cpus_write_unlock(void);
extern void cpus_read_lock(void);
extern void cpus_read_unlock(void);
-static inline void lockdep_assert_cpus_held(void) { }
+extern void lockdep_assert_cpus_held(void);
extern void cpu_hotplug_disable(void);
extern void cpu_hotplug_enable(void);
void clear_tasks_mm_cpumask(int cpu);
Index: b/kernel/cpu.c
===================================================================
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -27,6 +27,7 @@
#include <linux/smpboot.h>
#include <linux/relay.h>
#include <linux/slab.h>
+#include <linux/percpu-rwsem.h>
#include <trace/events/power.h>
#define CREATE_TRACE_POINTS
@@ -196,121 +197,41 @@ void cpu_maps_update_done(void)
mutex_unlock(&cpu_add_remove_lock);
}
-/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
+/*
+ * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
* Should always be manipulated under cpu_add_remove_lock
*/
static int cpu_hotplug_disabled;
#ifdef CONFIG_HOTPLUG_CPU
-static struct {
- struct task_struct *active_writer;
- /* wait queue to wake up the active_writer */
- wait_queue_head_t wq;
- /* verifies that no writer will get active while readers are active */
- struct mutex lock;
- /*
- * Also blocks the new readers during
- * an ongoing cpu hotplug operation.
- */
- atomic_t refcount;
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
- struct lockdep_map dep_map;
-#endif
-} cpu_hotplug = {
- .active_writer = NULL,
- .wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),
- .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
- .dep_map = STATIC_LOCKDEP_MAP_INIT("cpu_hotplug.dep_map", &cpu_hotplug.dep_map),
-#endif
-};
-
-/* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
-#define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
-#define cpuhp_lock_acquire_tryread() \
- lock_map_acquire_tryread(&cpu_hotplug.dep_map)
-#define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map)
-#define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map)
-
+DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
void cpus_read_lock(void)
{
- might_sleep();
- if (cpu_hotplug.active_writer == current)
- return;
- cpuhp_lock_acquire_read();
- mutex_lock(&cpu_hotplug.lock);
- atomic_inc(&cpu_hotplug.refcount);
- mutex_unlock(&cpu_hotplug.lock);
+ percpu_down_read(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_lock);
void cpus_read_unlock(void)
{
- int refcount;
-
- if (cpu_hotplug.active_writer == current)
- return;
-
- refcount = atomic_dec_return(&cpu_hotplug.refcount);
- if (WARN_ON(refcount < 0)) /* try to fix things up */
- atomic_inc(&cpu_hotplug.refcount);
-
- if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq))
- wake_up(&cpu_hotplug.wq);
-
- cpuhp_lock_release();
-
+ percpu_up_read(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_unlock);
-/*
- * This ensures that the hotplug operation can begin only when the
- * refcount goes to zero.
- *
- * Note that during a cpu-hotplug operation, the new readers, if any,
- * will be blocked by the cpu_hotplug.lock
- *
- * Since cpu_hotplug_begin() is always called after invoking
- * cpu_maps_update_begin(), we can be sure that only one writer is active.
- *
- * Note that theoretically, there is a possibility of a livelock:
- * - Refcount goes to zero, last reader wakes up the sleeping
- * writer.
- * - Last reader unlocks the cpu_hotplug.lock.
- * - A new reader arrives at this moment, bumps up the refcount.
- * - The writer acquires the cpu_hotplug.lock finds the refcount
- * non zero and goes to sleep again.
- *
- * However, this is very difficult to achieve in practice since
- * get_online_cpus() not an api which is called all that often.
- *
- */
void cpus_write_lock(void)
{
- DEFINE_WAIT(wait);
-
- cpu_hotplug.active_writer = current;
- cpuhp_lock_acquire();
-
- for (;;) {
- mutex_lock(&cpu_hotplug.lock);
- prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
- if (likely(!atomic_read(&cpu_hotplug.refcount)))
- break;
- mutex_unlock(&cpu_hotplug.lock);
- schedule();
- }
- finish_wait(&cpu_hotplug.wq, &wait);
+ percpu_down_write(&cpu_hotplug_lock);
}
void cpus_write_unlock(void)
{
- cpu_hotplug.active_writer = NULL;
- mutex_unlock(&cpu_hotplug.lock);
- cpuhp_lock_release();
+ percpu_up_write(&cpu_hotplug_lock);
+}
+
+void lockdep_assert_cpus_held(void)
+{
+ percpu_rwsem_assert_held(&cpu_hotplug_lock);
}
/*
@@ -344,8 +265,6 @@ void cpu_hotplug_enable(void)
EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
#endif /* CONFIG_HOTPLUG_CPU */
-/* Notifier wrappers for transitioning to state machine */
-
static int bringup_wait_for_ap(unsigned int cpu)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
next prev parent reply other threads:[~2017-05-24 8:29 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-24 8:15 [patch V3 00/32] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Thomas Gleixner
2017-05-24 8:15 ` [patch V3 01/32] cpu/hotplug: Provide cpus_read|write_[un]lock() Thomas Gleixner
2017-05-24 16:25 ` Paul E. McKenney
2017-05-26 8:31 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 02/32] cpu/hotplug: Provide lockdep_assert_cpus_held() Thomas Gleixner
2017-05-24 16:26 ` Paul E. McKenney
2017-05-26 8:32 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 03/32] cpu/hotplug: Provide cpuhp_setup/remove_state[_nocalls]_cpuslocked() Thomas Gleixner
2017-05-26 8:32 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 04/32] cpu/hotplug: Add __cpuhp_state_add_instance_cpuslocked() Thomas Gleixner
2017-05-26 8:33 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 05/32] stop_machine: Provide stop_machine_cpuslocked() Thomas Gleixner
2017-05-24 17:42 ` Paul E. McKenney
2017-05-26 8:33 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 06/32] padata: Make padata_alloc() static Thomas Gleixner
2017-05-26 8:34 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 07/32] padata: Avoid nested calls to cpus_read_lock() in pcrypt_init_padata() Thomas Gleixner
2017-05-26 8:35 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 08/32] x86/mtrr: Remove get_online_cpus() from mtrr_save_state() Thomas Gleixner
2017-05-26 8:35 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 09/32] cpufreq: Use cpuhp_setup_state_nocalls_cpuslocked() Thomas Gleixner
2017-05-26 8:36 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 10/32] KVM/PPC/Book3S HV: " Thomas Gleixner
2017-05-26 8:36 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 11/32] hwtracing/coresight-etm3x: " Thomas Gleixner
2017-05-25 16:46 ` Mathieu Poirier
2017-05-26 8:37 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 12/32] hwtracing/coresight-etm4x: " Thomas Gleixner
2017-05-25 16:47 ` Mathieu Poirier
2017-05-26 8:37 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 13/32] perf/x86/intel/cqm: Use cpuhp_setup_state_cpuslocked() Thomas Gleixner
2017-05-26 8:38 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 14/32] ARM/hw_breakpoint: " Thomas Gleixner
2017-05-26 8:38 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 15/32] s390/kernel: Use stop_machine_cpuslocked() Thomas Gleixner
2017-05-24 10:57 ` Heiko Carstens
2017-05-26 8:39 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 16/32] powerpc/powernv: " Thomas Gleixner
2017-05-26 8:40 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 17/32] cpu/hotplug: Use stop_machine_cpuslocked() in takedown_cpu() Thomas Gleixner
2017-05-26 8:40 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 18/32] x86/perf: Drop EXPORT of perf_check_microcode Thomas Gleixner
2017-05-26 8:41 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 19/32] perf/x86/intel: Drop get_online_cpus() in intel_snb_check_microcode() Thomas Gleixner
2017-05-26 8:41 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 20/32] PCI: Use cpu_hotplug_disable() instead of get_online_cpus() Thomas Gleixner
2017-05-26 8:42 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 21/32] PCI: Replace the racy recursion prevention Thomas Gleixner
2017-05-26 8:42 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 22/32] ACPI/processor: Use cpu_hotplug_disable() instead of get_online_cpus() Thomas Gleixner
2017-05-26 8:43 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 23/32] perf/tracing/cpuhotplug: Fix locking order Thomas Gleixner
2017-05-24 18:30 ` Paul E. McKenney
2017-05-24 18:47 ` Thomas Gleixner
2017-05-24 21:10 ` Paul E. McKenney
2017-05-30 11:22 ` Peter Zijlstra
2017-05-30 16:25 ` Paul E. McKenney
2017-05-26 8:43 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 24/32] jump_label: Reorder hotplug lock and jump_label_lock Thomas Gleixner
2017-05-24 12:50 ` David Miller
2017-05-26 8:44 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 25/32] kprobes: Cure hotplug lock ordering issues Thomas Gleixner
2017-05-24 15:54 ` Masami Hiramatsu
2017-05-26 7:47 ` Thomas Gleixner
2017-05-26 8:45 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 26/32] arm64: Prevent cpu hotplug rwsem recursion Thomas Gleixner
2017-05-26 8:45 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 27/32] arm: Prevent " Thomas Gleixner
2017-05-26 8:46 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 28/32] s390: " Thomas Gleixner
2017-05-24 10:57 ` Heiko Carstens
2017-05-26 8:46 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` Thomas Gleixner [this message]
2017-05-26 8:47 ` [tip:smp/hotplug] cpu/hotplug: Convert hotplug locking to percpu rwsem tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 30/32] sched: Provide is_percpu_thread() helper Thomas Gleixner
2017-05-26 8:47 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 31/32] acpi/processor: Prevent cpu hotplug deadlock Thomas Gleixner
2017-05-26 8:48 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 32/32] cpuhotplug: Link lock stacks for hotplug callbacks Thomas Gleixner
2017-05-26 8:48 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 16:22 ` [patch V3 00/32] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Paul E. McKenney
2017-05-26 7:03 ` Ingo Molnar
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