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![Oleg Nesterov](/assets/img/avatar_default.png)
cpu_stop_queue_work() checks stopper->enabled before it queues the work, but ->enabled == T can only guarantee cpu_stop_signal_done() if we race with cpu_down(). This is not enough for stop_two_cpus() or stop_machine(), they will deadlock if multi_cpu_stop() won't be called by one of the target CPU's. stop_machine/stop_cpus are fine, they rely on stop_cpus_mutex. But stop_two_cpus() has to check cpu_active() to avoid the same race with hotplug, and this check is very unobvious and probably not even correct if we race with cpu_up(). Change cpu_down() pass to clear ->enabled before cpu_stopper_thread() flushes the pending ->works and returns with KTHREAD_SHOULD_PARK set. Note also that smpboot_thread_call() calls cpu_stop_unpark() which sets enabled == T at CPU_ONLINE stage, so this CPU can't go away until cpu_stopper_thread() is called at least once. This all means that if cpu_stop_queue_work() succeeds, we know that work->fn() will be called. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Tejun Heo <tj@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: heiko.carstens@de.ibm.com Link: http://lkml.kernel.org/r/20151008145131.GA18139@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
140 lines
3.9 KiB
C
140 lines
3.9 KiB
C
#ifndef _LINUX_STOP_MACHINE
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#define _LINUX_STOP_MACHINE
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#include <linux/cpu.h>
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#include <linux/cpumask.h>
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#include <linux/smp.h>
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#include <linux/list.h>
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/*
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* stop_cpu[s]() is simplistic per-cpu maximum priority cpu
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* monopolization mechanism. The caller can specify a non-sleeping
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* function to be executed on a single or multiple cpus preempting all
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* other processes and monopolizing those cpus until it finishes.
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*
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* Resources for this mechanism are preallocated when a cpu is brought
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* up and requests are guaranteed to be served as long as the target
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* cpus are online.
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*/
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typedef int (*cpu_stop_fn_t)(void *arg);
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#ifdef CONFIG_SMP
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struct cpu_stop_work {
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struct list_head list; /* cpu_stopper->works */
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cpu_stop_fn_t fn;
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void *arg;
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struct cpu_stop_done *done;
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};
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int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg);
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int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg);
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void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
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struct cpu_stop_work *work_buf);
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int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);
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int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);
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void stop_machine_park(int cpu);
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#else /* CONFIG_SMP */
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#include <linux/workqueue.h>
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struct cpu_stop_work {
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struct work_struct work;
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cpu_stop_fn_t fn;
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void *arg;
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};
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static inline int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
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{
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int ret = -ENOENT;
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preempt_disable();
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if (cpu == smp_processor_id())
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ret = fn(arg);
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preempt_enable();
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return ret;
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}
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static void stop_one_cpu_nowait_workfn(struct work_struct *work)
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{
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struct cpu_stop_work *stwork =
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container_of(work, struct cpu_stop_work, work);
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preempt_disable();
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stwork->fn(stwork->arg);
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preempt_enable();
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}
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static inline void stop_one_cpu_nowait(unsigned int cpu,
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cpu_stop_fn_t fn, void *arg,
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struct cpu_stop_work *work_buf)
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{
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if (cpu == smp_processor_id()) {
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INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn);
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work_buf->fn = fn;
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work_buf->arg = arg;
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schedule_work(&work_buf->work);
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}
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}
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static inline int stop_cpus(const struct cpumask *cpumask,
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cpu_stop_fn_t fn, void *arg)
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{
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if (cpumask_test_cpu(raw_smp_processor_id(), cpumask))
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return stop_one_cpu(raw_smp_processor_id(), fn, arg);
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return -ENOENT;
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}
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static inline int try_stop_cpus(const struct cpumask *cpumask,
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cpu_stop_fn_t fn, void *arg)
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{
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return stop_cpus(cpumask, fn, arg);
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}
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#endif /* CONFIG_SMP */
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/*
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* stop_machine "Bogolock": stop the entire machine, disable
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* interrupts. This is a very heavy lock, which is equivalent to
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* grabbing every spinlock (and more). So the "read" side to such a
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* lock is anything which disables preemption.
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*/
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#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
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/**
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* stop_machine: freeze the machine on all CPUs and run this function
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* @fn: the function to run
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* @data: the data ptr for the @fn()
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* @cpus: the cpus to run the @fn() on (NULL = any online cpu)
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*
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* Description: This causes a thread to be scheduled on every cpu,
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* each of which disables interrupts. The result is that no one is
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* holding a spinlock or inside any other preempt-disabled region when
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* @fn() runs.
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*
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* This can be thought of as a very heavy write lock, equivalent to
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* grabbing every spinlock in the kernel. */
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int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
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int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
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const struct cpumask *cpus);
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#else /* CONFIG_STOP_MACHINE && CONFIG_SMP */
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static inline int stop_machine(cpu_stop_fn_t fn, void *data,
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const struct cpumask *cpus)
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{
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unsigned long flags;
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int ret;
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local_irq_save(flags);
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ret = fn(data);
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local_irq_restore(flags);
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return ret;
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}
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static inline int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
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const struct cpumask *cpus)
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{
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return stop_machine(fn, data, cpus);
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}
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#endif /* CONFIG_STOP_MACHINE && CONFIG_SMP */
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#endif /* _LINUX_STOP_MACHINE */
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