On 11/21/2017 08:30 PM, Jens Axboe wrote: > On 11/21/2017 12:15 PM, Christian Borntraeger wrote: >> >> >> On 11/21/2017 07:39 PM, Jens Axboe wrote: >>> On 11/21/2017 11:27 AM, Jens Axboe wrote: >>>> On 11/21/2017 11:12 AM, Christian Borntraeger wrote: >>>>> >>>>> >>>>> On 11/21/2017 07:09 PM, Jens Axboe wrote: >>>>>> On 11/21/2017 10:27 AM, Jens Axboe wrote: >>>>>>> On 11/21/2017 03:14 AM, Christian Borntraeger wrote: >>>>>>>> Bisect points to >>>>>>>> >>>>>>>> 1b5a7455d345b223d3a4658a9e5fce985b7998c1 is the first bad commit >>>>>>>> commit 1b5a7455d345b223d3a4658a9e5fce985b7998c1 >>>>>>>> Author: Christoph Hellwig <hch@xxxxxx> >>>>>>>> Date: Mon Jun 26 12:20:57 2017 +0200 >>>>>>>> >>>>>>>> blk-mq: Create hctx for each present CPU >>>>>>>> >>>>>>>> commit 4b855ad37194f7bdbb200ce7a1c7051fecb56a08 upstream. >>>>>>>> >>>>>>>> Currently we only create hctx for online CPUs, which can lead to a lot >>>>>>>> of churn due to frequent soft offline / online operations. Instead >>>>>>>> allocate one for each present CPU to avoid this and dramatically simplify >>>>>>>> the code. >>>>>>>> >>>>>>>> Signed-off-by: Christoph Hellwig <hch@xxxxxx> >>>>>>>> Reviewed-by: Jens Axboe <axboe@xxxxxxxxx> >>>>>>>> Cc: Keith Busch <keith.busch@xxxxxxxxx> >>>>>>>> Cc: linux-block@xxxxxxxxxxxxxxx >>>>>>>> Cc: linux-nvme@xxxxxxxxxxxxxxxxxxx >>>>>>>> Link: http://lkml.kernel.org/r/20170626102058.10200-3-hch@xxxxxx >>>>>>>> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> >>>>>>>> Cc: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx> >>>>>>>> Cc: Mike Galbraith <efault@xxxxxx> >>>>>>>> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> >>>>>>> >>>>>>> I wonder if we're simply not getting the masks updated correctly. I'll >>>>>>> take a look. >>>>>> >>>>>> Can't make it trigger here. We do init for each present CPU, which means >>>>>> that if I offline a few CPUs here and register a queue, those still show >>>>>> up as present (just offline) and get mapped accordingly. >>>>>> >>>>>> From the looks of it, your setup is different. If the CPU doesn't show >>>>>> up as present and it gets hotplugged, then I can see how this condition >>>>>> would trigger. What environment are you running this in? We might have >>>>>> to re-introduce the cpu hotplug notifier, right now we just monitor >>>>>> for a dead cpu and handle that. >>>>> >>>>> I am not doing a hot unplug and the replug, I use KVM and add a previously >>>>> not available CPU. >>>>> >>>>> in libvirt/virsh speak: >>>>> <vcpu placement='static' current='1'>4</vcpu> >>>> >>>> So that's why we run into problems. It's not present when we load the device, >>>> but becomes present and online afterwards. >>>> >>>> Christoph, we used to handle this just fine, your patch broke it. >>>> >>>> I'll see if I can come up with an appropriate fix. >>> >>> Can you try the below? >> >> >> It does prevent the crash but it seems that the new CPU is not "used " after the hotplug for mq: >> >> >> output with 2 cpus: >> /sys/kernel/debug/block/vda >> /sys/kernel/debug/block/vda/hctx0 >> /sys/kernel/debug/block/vda/hctx0/cpu0 >> /sys/kernel/debug/block/vda/hctx0/cpu0/completed >> /sys/kernel/debug/block/vda/hctx0/cpu0/merged >> /sys/kernel/debug/block/vda/hctx0/cpu0/dispatched >> /sys/kernel/debug/block/vda/hctx0/cpu0/rq_list >> /sys/kernel/debug/block/vda/hctx0/active >> /sys/kernel/debug/block/vda/hctx0/run >> /sys/kernel/debug/block/vda/hctx0/queued >> /sys/kernel/debug/block/vda/hctx0/dispatched >> /sys/kernel/debug/block/vda/hctx0/io_poll >> /sys/kernel/debug/block/vda/hctx0/sched_tags_bitmap >> /sys/kernel/debug/block/vda/hctx0/sched_tags >> /sys/kernel/debug/block/vda/hctx0/tags_bitmap >> /sys/kernel/debug/block/vda/hctx0/tags >> /sys/kernel/debug/block/vda/hctx0/ctx_map >> /sys/kernel/debug/block/vda/hctx0/busy >> /sys/kernel/debug/block/vda/hctx0/dispatch >> /sys/kernel/debug/block/vda/hctx0/flags >> /sys/kernel/debug/block/vda/hctx0/state >> /sys/kernel/debug/block/vda/sched >> /sys/kernel/debug/block/vda/sched/dispatch >> /sys/kernel/debug/block/vda/sched/starved >> /sys/kernel/debug/block/vda/sched/batching >> /sys/kernel/debug/block/vda/sched/write_next_rq >> /sys/kernel/debug/block/vda/sched/write_fifo_list >> /sys/kernel/debug/block/vda/sched/read_next_rq >> /sys/kernel/debug/block/vda/sched/read_fifo_list >> /sys/kernel/debug/block/vda/write_hints >> /sys/kernel/debug/block/vda/state >> /sys/kernel/debug/block/vda/requeue_list >> /sys/kernel/debug/block/vda/poll_stat > > Try this, basically just a revert. Yes, seems to work. Tested-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Do you know why the original commit made it into 4.12 stable? After all it has no Fixes tag and no cc stable- > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 11097477eeab..bc1950fa9ef6 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -37,6 +37,9 @@ > #include "blk-wbt.h" > #include "blk-mq-sched.h" > > +static DEFINE_MUTEX(all_q_mutex); > +static LIST_HEAD(all_q_list); > + > static bool blk_mq_poll(struct request_queue *q, blk_qc_t cookie); > static void blk_mq_poll_stats_start(struct request_queue *q); > static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb); > @@ -2114,8 +2117,8 @@ static void blk_mq_init_cpu_queues(struct request_queue *q, > INIT_LIST_HEAD(&__ctx->rq_list); > __ctx->queue = q; > > - /* If the cpu isn't present, the cpu is mapped to first hctx */ > - if (!cpu_present(i)) > + /* If the cpu isn't online, the cpu is mapped to first hctx */ > + if (!cpu_online(i)) > continue; > > hctx = blk_mq_map_queue(q, i); > @@ -2158,7 +2161,8 @@ static void blk_mq_free_map_and_requests(struct blk_mq_tag_set *set, > } > } > > -static void blk_mq_map_swqueue(struct request_queue *q) > +static void blk_mq_map_swqueue(struct request_queue *q, > + const struct cpumask *online_mask) > { > unsigned int i, hctx_idx; > struct blk_mq_hw_ctx *hctx; > @@ -2176,11 +2180,13 @@ static void blk_mq_map_swqueue(struct request_queue *q) > } > > /* > - * Map software to hardware queues. > - * > - * If the cpu isn't present, the cpu is mapped to first hctx. > + * Map software to hardware queues > */ > - for_each_present_cpu(i) { > + for_each_possible_cpu(i) { > + /* If the cpu isn't online, the cpu is mapped to first hctx */ > + if (!cpumask_test_cpu(i, online_mask)) > + continue; > + > hctx_idx = q->mq_map[i]; > /* unmapped hw queue can be remapped after CPU topo changed */ > if (!set->tags[hctx_idx] && > @@ -2495,8 +2501,16 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, > blk_queue_softirq_done(q, set->ops->complete); > > blk_mq_init_cpu_queues(q, set->nr_hw_queues); > + > + get_online_cpus(); > + mutex_lock(&all_q_mutex); > + > + list_add_tail(&q->all_q_node, &all_q_list); > blk_mq_add_queue_tag_set(set, q); > - blk_mq_map_swqueue(q); > + blk_mq_map_swqueue(q, cpu_online_mask); > + > + mutex_unlock(&all_q_mutex); > + put_online_cpus(); > > if (!(set->flags & BLK_MQ_F_NO_SCHED)) { > int ret; > @@ -2522,12 +2536,18 @@ void blk_mq_free_queue(struct request_queue *q) > { > struct blk_mq_tag_set *set = q->tag_set; > > + mutex_lock(&all_q_mutex); > + list_del_init(&q->all_q_node); > + mutex_unlock(&all_q_mutex); > + > blk_mq_del_queue_tag_set(q); > + > blk_mq_exit_hw_queues(q, set, set->nr_hw_queues); > } > > /* Basically redo blk_mq_init_queue with queue frozen */ > -static void blk_mq_queue_reinit(struct request_queue *q) > +static void blk_mq_queue_reinit(struct request_queue *q, > + const struct cpumask *online_mask) > { > WARN_ON_ONCE(!atomic_read(&q->mq_freeze_depth)); > > @@ -2539,12 +2559,76 @@ static void blk_mq_queue_reinit(struct request_queue *q) > * we should change hctx numa_node according to the new topology (this > * involves freeing and re-allocating memory, worth doing?) > */ > - blk_mq_map_swqueue(q); > + blk_mq_map_swqueue(q, online_mask); > > blk_mq_sysfs_register(q); > blk_mq_debugfs_register_hctxs(q); > } > > +/* > + * New online cpumask which is going to be set in this hotplug event. > + * Declare this cpumasks as global as cpu-hotplug operation is invoked > + * one-by-one and dynamically allocating this could result in a failure. > + */ > +static struct cpumask cpuhp_online_new; > + > +static void blk_mq_queue_reinit_work(void) > +{ > + struct request_queue *q; > + > + mutex_lock(&all_q_mutex); > + /* > + * We need to freeze and reinit all existing queues. Freezing > + * involves synchronous wait for an RCU grace period and doing it > + * one by one may take a long time. Start freezing all queues in > + * one swoop and then wait for the completions so that freezing can > + * take place in parallel. > + */ > + list_for_each_entry(q, &all_q_list, all_q_node) > + blk_freeze_queue_start(q); > + list_for_each_entry(q, &all_q_list, all_q_node) > + blk_mq_freeze_queue_wait(q); > + > + list_for_each_entry(q, &all_q_list, all_q_node) > + blk_mq_queue_reinit(q, &cpuhp_online_new); > + > + list_for_each_entry(q, &all_q_list, all_q_node) > + blk_mq_unfreeze_queue(q); > + > + mutex_unlock(&all_q_mutex); > +} > + > +static int blk_mq_queue_reinit_dead(unsigned int cpu) > +{ > + cpumask_copy(&cpuhp_online_new, cpu_online_mask); > + blk_mq_queue_reinit_work(); > + return 0; > +} > + > +/* > + * Before hotadded cpu starts handling requests, new mappings must be > + * established. Otherwise, these requests in hw queue might never be > + * dispatched. > + * > + * For example, there is a single hw queue (hctx) and two CPU queues (ctx0 > + * for CPU0, and ctx1 for CPU1). > + * > + * Now CPU1 is just onlined and a request is inserted into ctx1->rq_list > + * and set bit0 in pending bitmap as ctx1->index_hw is still zero. > + * > + * And then while running hw queue, blk_mq_flush_busy_ctxs() finds bit0 is set > + * in pending bitmap and tries to retrieve requests in hctx->ctxs[0]->rq_list. > + * But htx->ctxs[0] is a pointer to ctx0, so the request in ctx1->rq_list is > + * ignored. > + */ > +static int blk_mq_queue_reinit_prepare(unsigned int cpu) > +{ > + cpumask_copy(&cpuhp_online_new, cpu_online_mask); > + cpumask_set_cpu(cpu, &cpuhp_online_new); > + blk_mq_queue_reinit_work(); > + return 0; > +} > + > static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set) > { > int i; > @@ -2757,7 +2841,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, > blk_mq_update_queue_map(set); > list_for_each_entry(q, &set->tag_list, tag_set_list) { > blk_mq_realloc_hw_ctxs(set, q); > - blk_mq_queue_reinit(q); > + blk_mq_queue_reinit(q, cpu_online_mask); > } > > list_for_each_entry(q, &set->tag_list, tag_set_list) > @@ -2966,6 +3050,16 @@ static bool blk_mq_poll(struct request_queue *q, blk_qc_t cookie) > return __blk_mq_poll(hctx, rq); > } > > +void blk_mq_disable_hotplug(void) > +{ > + mutex_lock(&all_q_mutex); > +} > + > +void blk_mq_enable_hotplug(void) > +{ > + mutex_unlock(&all_q_mutex); > +} > + > static int __init blk_mq_init(void) > { > /* > @@ -2976,6 +3070,10 @@ static int __init blk_mq_init(void) > > cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL, > blk_mq_hctx_notify_dead); > + > + cpuhp_setup_state_nocalls(CPUHP_BLK_MQ_PREPARE, "block/mq:prepare", > + blk_mq_queue_reinit_prepare, > + blk_mq_queue_reinit_dead); > return 0; > } > subsys_initcall(blk_mq_init); > diff --git a/block/blk-mq.h b/block/blk-mq.h > index 6c7c3ff5bf62..83b13ef1915e 100644 > --- a/block/blk-mq.h > +++ b/block/blk-mq.h > @@ -59,6 +59,11 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, > void blk_mq_request_bypass_insert(struct request *rq, bool run_queue); > void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx, > struct list_head *list); > +/* > + * CPU hotplug helpers > + */ > +void blk_mq_enable_hotplug(void); > +void blk_mq_disable_hotplug(void); > > /* > * CPU -> queue mappings > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h > index 201ab7267986..c31d4e3bf6d0 100644 > --- a/include/linux/cpuhotplug.h > +++ b/include/linux/cpuhotplug.h > @@ -76,6 +76,7 @@ enum cpuhp_state { > CPUHP_XEN_EVTCHN_PREPARE, > CPUHP_ARM_SHMOBILE_SCU_PREPARE, > CPUHP_SH_SH3X_PREPARE, > + CPUHP_BLK_MQ_PREPARE, > CPUHP_NET_FLOW_PREPARE, > CPUHP_TOPOLOGY_PREPARE, > CPUHP_NET_IUCV_PREPARE, >
