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SubjectRe: [PATCH 08/15] block, dax, pmem: reference counting infrastructure
Date
On Fri, 2015-09-25 at 04:32 -0700, Christoph Hellwig wrote:
> On Thu, Sep 24, 2015 at 05:03:18PM -0700, Dan Williams wrote:
> > That makes sense to me, especially because drivers/nvdimm/blk.c is
> > broken in the same way as drivers/nvdimm/pmem.c and it would be
> > awkward to have it use blk_dax_get() / blk_dax_put(). The
> > percpu_refcount should be valid for all queues and it will only ever
> > be > 1 in the blk_mq and libnvdimm cases (for now). Will fix.
>
> Looking at this a bit more it might actually make sense to grab the
> referene in common code before calling into ->make_request.
>
> Jens, any opinion on that?

...this works for me:

8<-----
Subject: [PATCH] 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>
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;
--
2.1.0


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