block: generic request_queue reference counting

Allow pmem, and other synchronous/bio-based block drivers, to fallback
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
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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

5 files changed, 101 insertions, 73 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 2eb722d48773..9b4d735cb5b8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -554,13 +554,10 @@ 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);
 
@@ -570,6 +567,7 @@ void blk_cleanup_queue(struct request_queue *q)
 
         if (q->mq_ops)
                 blk_mq_free_queue(q);
+        percpu_ref_exit(&q->q_usage_counter);
 
         spin_lock_irq(lock);
         if (q->queue_lock != &q->__queue_lock)
@@ -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 788fffd9b409..6f57a110289c 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -413,12 +413,6 @@ 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 d921cd5177f5..6c240712553a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -78,47 +78,13 @@ 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);
         }
 }
@@ -126,18 +92,34 @@ 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)
@@ -147,7 +129,7 @@ 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);
         }
 }
@@ -256,7 +238,7 @@ 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);
 
@@ -279,7 +261,7 @@ 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;
@@ -298,7 +280,7 @@ 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)
@@ -1177,11 +1159,7 @@ 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);
 
@@ -2000,14 +1978,6 @@ 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);
 
@@ -2088,8 +2058,6 @@ 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);
 }
 
 /* Basically redo blk_mq_init_queue with queue frozen */
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);