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Date: Sun, 4 Oct 2015 15:52:54 +0800
Message-ID: <CACVXFVNRzR0339Zq7TG32Z1WboehAvGuaPeijW1t9AjRvLZrBQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] block: generic request_queue reference counting
From: Ming Lei <tom.leiming@gmail.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>, Keith Busch <keith.busch@intel.com>,
        ross.zwisler@linux.intel.com, linux-nvdimm@ml01.01.org,
        Christoph Hellwig <hch@lst.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Sep 30, 2015 at 8:41 AM, Dan Williams <dan.j.williams@intel.com> wrote:
> Allow pmem, and other synchronous/bio-based block drivers, to fallback

Just a bit curious, why not extend it for all(both synchronous and
asynchrounous) bio-based drivers? As you mentioned in introductory
message, all bio based drivers may have this kind of problem.

One idea I thought of is to hold the usage counter in bio life time,
instead of request's life time like in blk-mq.

> on a per-cpu reference count managed by the core for tracking queue
> live/dead state.
>
> The existing per-cpu reference count for the blk_mq case is promoted to
> be used in all block i/o scenarios.  This involves initializing it by
> default, waiting for it to drop to zero at exit, and holding a live
> reference over the invocation of q->make_request_fn() in

It isn't enough for asynchrounous bio drivers.

> generic_make_request().  The blk_mq code continues to take its own
> reference per blk_mq request and retains the ability to freeze the
> queue, but the check that the queue is frozen is moved to
> generic_make_request().
>
> This fixes crash signatures like the following:
>
>  BUG: unable to handle kernel paging request at ffff880140000000
>  [..]
>  Call Trace:
>   [<ffffffff8145e8bf>] ? copy_user_handle_tail+0x5f/0x70
>   [<ffffffffa004e1e0>] pmem_do_bvec.isra.11+0x70/0xf0 [nd_pmem]
>   [<ffffffffa004e331>] pmem_make_request+0xd1/0x200 [nd_pmem]
>   [<ffffffff811c3162>] ? mempool_alloc+0x72/0x1a0
>   [<ffffffff8141f8b6>] generic_make_request+0xd6/0x110
>   [<ffffffff8141f966>] submit_bio+0x76/0x170
>   [<ffffffff81286dff>] submit_bh_wbc+0x12f/0x160
>   [<ffffffff81286e62>] submit_bh+0x12/0x20
>   [<ffffffff813395bd>] jbd2_write_superblock+0x8d/0x170
>   [<ffffffff8133974d>] jbd2_mark_journal_empty+0x5d/0x90
>   [<ffffffff813399cb>] jbd2_journal_destroy+0x24b/0x270
>   [<ffffffff810bc4ca>] ? put_pwq_unlocked+0x2a/0x30
>   [<ffffffff810bc6f5>] ? destroy_workqueue+0x225/0x250
>   [<ffffffff81303494>] ext4_put_super+0x64/0x360
>   [<ffffffff8124ab1a>] generic_shutdown_super+0x6a/0xf0
>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Keith Busch <keith.busch@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  block/blk-core.c       |   71 +++++++++++++++++++++++++++++++++++++------
>  block/blk-mq-sysfs.c   |    6 ----
>  block/blk-mq.c         |   80 ++++++++++++++----------------------------------
>  block/blk-sysfs.c      |    3 +-
>  block/blk.h            |   14 ++++++++
>  include/linux/blk-mq.h |    1 -
>  include/linux/blkdev.h |    2 +
>  7 files changed, 102 insertions(+), 75 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 2eb722d48773..6062550baaef 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -554,19 +554,17 @@ void blk_cleanup_queue(struct request_queue *q)
>          * Drain all requests queued before DYING marking. Set DEAD flag to
>          * prevent that q->request_fn() gets invoked after draining finished.
>          */
> -       if (q->mq_ops) {
> -               blk_mq_freeze_queue(q);
> -               spin_lock_irq(lock);
> -       } else {
> -               spin_lock_irq(lock);
> +       blk_freeze_queue(q);
> +       spin_lock_irq(lock);
> +       if (!q->mq_ops)
>                 __blk_drain_queue(q, true);
> -       }
>         queue_flag_set(QUEUE_FLAG_DEAD, q);
>         spin_unlock_irq(lock);
>
>         /* @q won't process any more request, flush async actions */
>         del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
>         blk_sync_queue(q);
> +       percpu_ref_exit(&q->q_usage_counter);
>
>         if (q->mq_ops)
>                 blk_mq_free_queue(q);
> @@ -629,6 +627,40 @@ struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
>  }
>  EXPORT_SYMBOL(blk_alloc_queue);
>
> +int blk_queue_enter(struct request_queue *q, gfp_t gfp)
> +{
> +       while (true) {
> +               int ret;
> +
> +               if (percpu_ref_tryget_live(&q->q_usage_counter))
> +                       return 0;
> +
> +               if (!(gfp & __GFP_WAIT))
> +                       return -EBUSY;
> +
> +               ret = wait_event_interruptible(q->mq_freeze_wq,
> +                               !atomic_read(&q->mq_freeze_depth) ||
> +                               blk_queue_dying(q));
> +               if (blk_queue_dying(q))
> +                       return -ENODEV;
> +               if (ret)
> +                       return ret;
> +       }
> +}
> +
> +void blk_queue_exit(struct request_queue *q)
> +{
> +       percpu_ref_put(&q->q_usage_counter);
> +}
> +
> +static void blk_queue_usage_counter_release(struct percpu_ref *ref)
> +{
> +       struct request_queue *q =
> +               container_of(ref, struct request_queue, q_usage_counter);
> +
> +       wake_up_all(&q->mq_freeze_wq);
> +}
> +
>  struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
>  {
>         struct request_queue *q;
> @@ -690,11 +722,22 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
>
>         init_waitqueue_head(&q->mq_freeze_wq);
>
> -       if (blkcg_init_queue(q))
> +       /*
> +        * Init percpu_ref in atomic mode so that it's faster to shutdown.
> +        * See blk_register_queue() for details.
> +        */
> +       if (percpu_ref_init(&q->q_usage_counter,
> +                               blk_queue_usage_counter_release,
> +                               PERCPU_REF_INIT_ATOMIC, GFP_KERNEL))
>                 goto fail_bdi;
>
> +       if (blkcg_init_queue(q))
> +               goto fail_ref;
> +
>         return q;
>
> +fail_ref:
> +       percpu_ref_exit(&q->q_usage_counter);
>  fail_bdi:
>         bdi_destroy(&q->backing_dev_info);
>  fail_split:
> @@ -1966,9 +2009,19 @@ void generic_make_request(struct bio *bio)
>         do {
>                 struct request_queue *q = bdev_get_queue(bio->bi_bdev);
>
> -               q->make_request_fn(q, bio);
> +               if (likely(blk_queue_enter(q, __GFP_WAIT) == 0)) {
> +
> +                       q->make_request_fn(q, bio);
> +
> +                       blk_queue_exit(q);
>
> -               bio = bio_list_pop(current->bio_list);
> +                       bio = bio_list_pop(current->bio_list);
> +               } else {
> +                       struct bio *bio_next = bio_list_pop(current->bio_list);
> +
> +                       bio_io_error(bio);
> +                       bio = bio_next;
> +               }
>         } while (bio);
>         current->bio_list = NULL; /* deactivate */
>  }
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index 279c5d674edf..731b6eecce82 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -412,12 +412,6 @@ static void blk_mq_sysfs_init(struct request_queue *q)
>                 kobject_init(&ctx->kobj, &blk_mq_ctx_ktype);
>  }
>
> -/* see blk_register_queue() */
> -void blk_mq_finish_init(struct request_queue *q)
> -{
> -       percpu_ref_switch_to_percpu(&q->mq_usage_counter);
> -}
> -
>  int blk_mq_register_disk(struct gendisk *disk)
>  {
>         struct device *dev = disk_to_dev(disk);
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f2d67b4047a0..6d91894cf85e 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -77,47 +77,13 @@ static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx *hctx,
>         clear_bit(CTX_TO_BIT(hctx, ctx), &bm->word);
>  }
>
> -static int blk_mq_queue_enter(struct request_queue *q, gfp_t gfp)
> -{
> -       while (true) {
> -               int ret;
> -
> -               if (percpu_ref_tryget_live(&q->mq_usage_counter))
> -                       return 0;
> -
> -               if (!(gfp & __GFP_WAIT))
> -                       return -EBUSY;
> -
> -               ret = wait_event_interruptible(q->mq_freeze_wq,
> -                               !atomic_read(&q->mq_freeze_depth) ||
> -                               blk_queue_dying(q));
> -               if (blk_queue_dying(q))
> -                       return -ENODEV;
> -               if (ret)
> -                       return ret;
> -       }
> -}
> -
> -static void blk_mq_queue_exit(struct request_queue *q)
> -{
> -       percpu_ref_put(&q->mq_usage_counter);
> -}
> -
> -static void blk_mq_usage_counter_release(struct percpu_ref *ref)
> -{
> -       struct request_queue *q =
> -               container_of(ref, struct request_queue, mq_usage_counter);
> -
> -       wake_up_all(&q->mq_freeze_wq);
> -}
> -
>  void blk_mq_freeze_queue_start(struct request_queue *q)
>  {
>         int freeze_depth;
>
>         freeze_depth = atomic_inc_return(&q->mq_freeze_depth);
>         if (freeze_depth == 1) {
> -               percpu_ref_kill(&q->mq_usage_counter);
> +               percpu_ref_kill(&q->q_usage_counter);
>                 blk_mq_run_hw_queues(q, false);
>         }
>  }
> @@ -125,18 +91,34 @@ EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_start);
>
>  static void blk_mq_freeze_queue_wait(struct request_queue *q)
>  {
> -       wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
> +       wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter));
>  }
>
>  /*
>   * Guarantee no request is in use, so we can change any data structure of
>   * the queue afterward.
>   */
> -void blk_mq_freeze_queue(struct request_queue *q)
> +void blk_freeze_queue(struct request_queue *q)
>  {
> +       /*
> +        * In the !blk_mq case we are only calling this to kill the
> +        * q_usage_counter, otherwise this increases the freeze depth
> +        * and waits for it to return to zero.  For this reason there is
> +        * no blk_unfreeze_queue(), and blk_freeze_queue() is not
> +        * exported to drivers as the only user for unfreeze is blk_mq.
> +        */
>         blk_mq_freeze_queue_start(q);
>         blk_mq_freeze_queue_wait(q);
>  }
> +
> +void blk_mq_freeze_queue(struct request_queue *q)
> +{
> +       /*
> +        * ...just an alias to keep freeze and unfreeze actions balanced
> +        * in the blk_mq_* namespace
> +        */
> +       blk_freeze_queue(q);
> +}
>  EXPORT_SYMBOL_GPL(blk_mq_freeze_queue);
>
>  void blk_mq_unfreeze_queue(struct request_queue *q)
> @@ -146,7 +128,7 @@ void blk_mq_unfreeze_queue(struct request_queue *q)
>         freeze_depth = atomic_dec_return(&q->mq_freeze_depth);
>         WARN_ON_ONCE(freeze_depth < 0);
>         if (!freeze_depth) {
> -               percpu_ref_reinit(&q->mq_usage_counter);
> +               percpu_ref_reinit(&q->q_usage_counter);
>                 wake_up_all(&q->mq_freeze_wq);
>         }
>  }
> @@ -255,7 +237,7 @@ struct request *blk_mq_alloc_request(struct request_queue *q, int rw, gfp_t gfp,
>         struct blk_mq_alloc_data alloc_data;
>         int ret;
>
> -       ret = blk_mq_queue_enter(q, gfp);
> +       ret = blk_queue_enter(q, gfp);
>         if (ret)
>                 return ERR_PTR(ret);
>
> @@ -278,7 +260,7 @@ struct request *blk_mq_alloc_request(struct request_queue *q, int rw, gfp_t gfp,
>         }
>         blk_mq_put_ctx(ctx);
>         if (!rq) {
> -               blk_mq_queue_exit(q);
> +               blk_queue_exit(q);
>                 return ERR_PTR(-EWOULDBLOCK);
>         }
>         return rq;
> @@ -297,7 +279,7 @@ static void __blk_mq_free_request(struct blk_mq_hw_ctx *hctx,
>
>         clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
>         blk_mq_put_tag(hctx, tag, &ctx->last_tag);
> -       blk_mq_queue_exit(q);
> +       blk_queue_exit(q);
>  }
>
>  void blk_mq_free_hctx_request(struct blk_mq_hw_ctx *hctx, struct request *rq)
> @@ -1184,11 +1166,7 @@ static struct request *blk_mq_map_request(struct request_queue *q,
>         int rw = bio_data_dir(bio);
>         struct blk_mq_alloc_data alloc_data;
>
> -       if (unlikely(blk_mq_queue_enter(q, GFP_KERNEL))) {
> -               bio_io_error(bio);
> -               return NULL;
> -       }
> -
> +       blk_queue_enter_live(q);
>         ctx = blk_mq_get_ctx(q);
>         hctx = q->mq_ops->map_queue(q, ctx->cpu);
>
> @@ -1979,14 +1957,6 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
>                 hctxs[i]->queue_num = i;
>         }
>
> -       /*
> -        * Init percpu_ref in atomic mode so that it's faster to shutdown.
> -        * See blk_register_queue() for details.
> -        */
> -       if (percpu_ref_init(&q->mq_usage_counter, blk_mq_usage_counter_release,
> -                           PERCPU_REF_INIT_ATOMIC, GFP_KERNEL))
> -               goto err_hctxs;
> -
>         setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);
>         blk_queue_rq_timeout(q, set->timeout ? set->timeout : 30 * HZ);
>
> @@ -2062,8 +2032,6 @@ void blk_mq_free_queue(struct request_queue *q)
>         blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
>         blk_mq_free_hw_queues(q, set);
>
> -       percpu_ref_exit(&q->mq_usage_counter);
> -
>         kfree(q->mq_map);
>
>         q->mq_map = NULL;
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 3e44a9da2a13..61fc2633bbea 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -599,9 +599,8 @@ int blk_register_queue(struct gendisk *disk)
>          */
>         if (!blk_queue_init_done(q)) {
>                 queue_flag_set_unlocked(QUEUE_FLAG_INIT_DONE, q);
> +               percpu_ref_switch_to_percpu(&q->q_usage_counter);
>                 blk_queue_bypass_end(q);
> -               if (q->mq_ops)
> -                       blk_mq_finish_init(q);
>         }
>
>         ret = blk_trace_init_sysfs(dev);
> diff --git a/block/blk.h b/block/blk.h
> index 98614ad37c81..5b2cd393afbe 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -72,6 +72,20 @@ void blk_dequeue_request(struct request *rq);
>  void __blk_queue_free_tags(struct request_queue *q);
>  bool __blk_end_bidi_request(struct request *rq, int error,
>                             unsigned int nr_bytes, unsigned int bidi_bytes);
> +int blk_queue_enter(struct request_queue *q, gfp_t gfp);
> +void blk_queue_exit(struct request_queue *q);
> +void blk_freeze_queue(struct request_queue *q);
> +
> +static inline void blk_queue_enter_live(struct request_queue *q)
> +{
> +       /*
> +        * Given that running in generic_make_request() context
> +        * guarantees that a live reference against q_usage_counter has
> +        * been established, further references under that same context
> +        * need not check that the queue has been frozen (marked dead).
> +        */
> +       percpu_ref_get(&q->q_usage_counter);
> +}
>
>  void blk_rq_timed_out_timer(unsigned long data);
>  unsigned long blk_rq_timeout(unsigned long timeout);
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 37d1602c4f7a..25ce763fbb81 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -167,7 +167,6 @@ enum {
>  struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *);
>  struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
>                                                   struct request_queue *q);
> -void blk_mq_finish_init(struct request_queue *q);
>  int blk_mq_register_disk(struct gendisk *);
>  void blk_mq_unregister_disk(struct gendisk *);
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 99da9ebc7377..0a0def66c61e 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -450,7 +450,7 @@ struct request_queue {
>  #endif
>         struct rcu_head         rcu_head;
>         wait_queue_head_t       mq_freeze_wq;
> -       struct percpu_ref       mq_usage_counter;
> +       struct percpu_ref       q_usage_counter;
>         struct list_head        all_q_node;
>
>         struct blk_mq_tag_set   *tag_set;
>
> --
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-- 
Ming Lei