X-Git-Url: http://pileus.org/git/?a=blobdiff_plain;f=kernel%2Fstop_machine.c;h=84571e09c9079e8887f73a0f24beefe58e00ff77;hb=0ca9fff744c8ae22401d1ef10a378588afd55abc;hp=c09f2955ae3055b42f1edde601ee1eb431bfc18a;hpb=191a712090bb8a10e6f129360eeed2d68f3d4c9a;p=~andy%2Flinux diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index c09f2955ae3..84571e09c90 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -20,6 +20,7 @@ #include #include #include +#include /* * Structure to determine completion condition and record errors. May @@ -43,6 +44,14 @@ static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper); static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task); static bool stop_machine_initialized = false; +/* + * Avoids a race between stop_two_cpus and global stop_cpus, where + * the stoppers could get queued up in reverse order, leading to + * system deadlock. Using an lglock means stop_two_cpus remains + * relatively cheap. + */ +DEFINE_STATIC_LGLOCK(stop_cpus_lock); + static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo) { memset(done, 0, sizeof(*done)); @@ -115,6 +124,184 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) return done.executed ? done.ret : -ENOENT; } +/* This controls the threads on each CPU. */ +enum multi_stop_state { + /* Dummy starting state for thread. */ + MULTI_STOP_NONE, + /* Awaiting everyone to be scheduled. */ + MULTI_STOP_PREPARE, + /* Disable interrupts. */ + MULTI_STOP_DISABLE_IRQ, + /* Run the function */ + MULTI_STOP_RUN, + /* Exit */ + MULTI_STOP_EXIT, +}; + +struct multi_stop_data { + int (*fn)(void *); + void *data; + /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */ + unsigned int num_threads; + const struct cpumask *active_cpus; + + enum multi_stop_state state; + atomic_t thread_ack; +}; + +static void set_state(struct multi_stop_data *msdata, + enum multi_stop_state newstate) +{ + /* Reset ack counter. */ + atomic_set(&msdata->thread_ack, msdata->num_threads); + smp_wmb(); + msdata->state = newstate; +} + +/* Last one to ack a state moves to the next state. */ +static void ack_state(struct multi_stop_data *msdata) +{ + if (atomic_dec_and_test(&msdata->thread_ack)) + set_state(msdata, msdata->state + 1); +} + +/* This is the cpu_stop function which stops the CPU. */ +static int multi_cpu_stop(void *data) +{ + struct multi_stop_data *msdata = data; + enum multi_stop_state curstate = MULTI_STOP_NONE; + int cpu = smp_processor_id(), err = 0; + unsigned long flags; + bool is_active; + + /* + * When called from stop_machine_from_inactive_cpu(), irq might + * already be disabled. Save the state and restore it on exit. + */ + local_save_flags(flags); + + if (!msdata->active_cpus) + is_active = cpu == cpumask_first(cpu_online_mask); + else + is_active = cpumask_test_cpu(cpu, msdata->active_cpus); + + /* Simple state machine */ + do { + /* Chill out and ensure we re-read multi_stop_state. */ + cpu_relax(); + if (msdata->state != curstate) { + curstate = msdata->state; + switch (curstate) { + case MULTI_STOP_DISABLE_IRQ: + local_irq_disable(); + hard_irq_disable(); + break; + case MULTI_STOP_RUN: + if (is_active) + err = msdata->fn(msdata->data); + break; + default: + break; + } + ack_state(msdata); + } + } while (curstate != MULTI_STOP_EXIT); + + local_irq_restore(flags); + return err; +} + +struct irq_cpu_stop_queue_work_info { + int cpu1; + int cpu2; + struct cpu_stop_work *work1; + struct cpu_stop_work *work2; +}; + +/* + * This function is always run with irqs and preemption disabled. + * This guarantees that both work1 and work2 get queued, before + * our local migrate thread gets the chance to preempt us. + */ +static void irq_cpu_stop_queue_work(void *arg) +{ + struct irq_cpu_stop_queue_work_info *info = arg; + cpu_stop_queue_work(info->cpu1, info->work1); + cpu_stop_queue_work(info->cpu2, info->work2); +} + +/** + * stop_two_cpus - stops two cpus + * @cpu1: the cpu to stop + * @cpu2: the other cpu to stop + * @fn: function to execute + * @arg: argument to @fn + * + * Stops both the current and specified CPU and runs @fn on one of them. + * + * returns when both are completed. + */ +int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg) +{ + struct cpu_stop_done done; + struct cpu_stop_work work1, work2; + struct irq_cpu_stop_queue_work_info call_args; + struct multi_stop_data msdata; + + preempt_disable(); + msdata = (struct multi_stop_data){ + .fn = fn, + .data = arg, + .num_threads = 2, + .active_cpus = cpumask_of(cpu1), + }; + + work1 = work2 = (struct cpu_stop_work){ + .fn = multi_cpu_stop, + .arg = &msdata, + .done = &done + }; + + call_args = (struct irq_cpu_stop_queue_work_info){ + .cpu1 = cpu1, + .cpu2 = cpu2, + .work1 = &work1, + .work2 = &work2, + }; + + cpu_stop_init_done(&done, 2); + set_state(&msdata, MULTI_STOP_PREPARE); + + /* + * If we observe both CPUs active we know _cpu_down() cannot yet have + * queued its stop_machine works and therefore ours will get executed + * first. Or its not either one of our CPUs that's getting unplugged, + * in which case we don't care. + * + * This relies on the stopper workqueues to be FIFO. + */ + if (!cpu_active(cpu1) || !cpu_active(cpu2)) { + preempt_enable(); + return -ENOENT; + } + + lg_local_lock(&stop_cpus_lock); + /* + * Queuing needs to be done by the lowest numbered CPU, to ensure + * that works are always queued in the same order on every CPU. + * This prevents deadlocks. + */ + smp_call_function_single(min(cpu1, cpu2), + &irq_cpu_stop_queue_work, + &call_args, 0); + lg_local_unlock(&stop_cpus_lock); + preempt_enable(); + + wait_for_completion(&done.completion); + + return done.executed ? done.ret : -ENOENT; +} + /** * stop_one_cpu_nowait - stop a cpu but don't wait for completion * @cpu: cpu to stop @@ -159,10 +346,10 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask, * preempted by a stopper which might wait for other stoppers * to enter @fn which can lead to deadlock. */ - preempt_disable(); + lg_global_lock(&stop_cpus_lock); for_each_cpu(cpu, cpumask) cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu)); - preempt_enable(); + lg_global_unlock(&stop_cpus_lock); } static int __stop_cpus(const struct cpumask *cpumask, @@ -359,98 +546,14 @@ early_initcall(cpu_stop_init); #ifdef CONFIG_STOP_MACHINE -/* This controls the threads on each CPU. */ -enum stopmachine_state { - /* Dummy starting state for thread. */ - STOPMACHINE_NONE, - /* Awaiting everyone to be scheduled. */ - STOPMACHINE_PREPARE, - /* Disable interrupts. */ - STOPMACHINE_DISABLE_IRQ, - /* Run the function */ - STOPMACHINE_RUN, - /* Exit */ - STOPMACHINE_EXIT, -}; - -struct stop_machine_data { - int (*fn)(void *); - void *data; - /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */ - unsigned int num_threads; - const struct cpumask *active_cpus; - - enum stopmachine_state state; - atomic_t thread_ack; -}; - -static void set_state(struct stop_machine_data *smdata, - enum stopmachine_state newstate) -{ - /* Reset ack counter. */ - atomic_set(&smdata->thread_ack, smdata->num_threads); - smp_wmb(); - smdata->state = newstate; -} - -/* Last one to ack a state moves to the next state. */ -static void ack_state(struct stop_machine_data *smdata) -{ - if (atomic_dec_and_test(&smdata->thread_ack)) - set_state(smdata, smdata->state + 1); -} - -/* This is the cpu_stop function which stops the CPU. */ -static int stop_machine_cpu_stop(void *data) -{ - struct stop_machine_data *smdata = data; - enum stopmachine_state curstate = STOPMACHINE_NONE; - int cpu = smp_processor_id(), err = 0; - unsigned long flags; - bool is_active; - - /* - * When called from stop_machine_from_inactive_cpu(), irq might - * already be disabled. Save the state and restore it on exit. - */ - local_save_flags(flags); - - if (!smdata->active_cpus) - is_active = cpu == cpumask_first(cpu_online_mask); - else - is_active = cpumask_test_cpu(cpu, smdata->active_cpus); - - /* Simple state machine */ - do { - /* Chill out and ensure we re-read stopmachine_state. */ - cpu_relax(); - if (smdata->state != curstate) { - curstate = smdata->state; - switch (curstate) { - case STOPMACHINE_DISABLE_IRQ: - local_irq_disable(); - hard_irq_disable(); - break; - case STOPMACHINE_RUN: - if (is_active) - err = smdata->fn(smdata->data); - break; - default: - break; - } - ack_state(smdata); - } - } while (curstate != STOPMACHINE_EXIT); - - local_irq_restore(flags); - return err; -} - int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) { - struct stop_machine_data smdata = { .fn = fn, .data = data, - .num_threads = num_online_cpus(), - .active_cpus = cpus }; + struct multi_stop_data msdata = { + .fn = fn, + .data = data, + .num_threads = num_online_cpus(), + .active_cpus = cpus, + }; if (!stop_machine_initialized) { /* @@ -461,7 +564,7 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) unsigned long flags; int ret; - WARN_ON_ONCE(smdata.num_threads != 1); + WARN_ON_ONCE(msdata.num_threads != 1); local_irq_save(flags); hard_irq_disable(); @@ -472,8 +575,8 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) } /* Set the initial state and stop all online cpus. */ - set_state(&smdata, STOPMACHINE_PREPARE); - return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata); + set_state(&msdata, MULTI_STOP_PREPARE); + return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata); } int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) @@ -513,25 +616,25 @@ EXPORT_SYMBOL_GPL(stop_machine); int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data, const struct cpumask *cpus) { - struct stop_machine_data smdata = { .fn = fn, .data = data, + struct multi_stop_data msdata = { .fn = fn, .data = data, .active_cpus = cpus }; struct cpu_stop_done done; int ret; /* Local CPU must be inactive and CPU hotplug in progress. */ BUG_ON(cpu_active(raw_smp_processor_id())); - smdata.num_threads = num_active_cpus() + 1; /* +1 for local */ + msdata.num_threads = num_active_cpus() + 1; /* +1 for local */ /* No proper task established and can't sleep - busy wait for lock. */ while (!mutex_trylock(&stop_cpus_mutex)) cpu_relax(); /* Schedule work on other CPUs and execute directly for local CPU */ - set_state(&smdata, STOPMACHINE_PREPARE); + set_state(&msdata, MULTI_STOP_PREPARE); cpu_stop_init_done(&done, num_active_cpus()); - queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata, + queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata, &done); - ret = stop_machine_cpu_stop(&smdata); + ret = multi_cpu_stop(&msdata); /* Busy wait for completion. */ while (!completion_done(&done.completion))