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Re: [dm-devel] [RFC PATCH v2] dm mpath: add a queue_if_no_path timeout



On 11/01/13 10:58, Junichi Nomura wrote:
> On 10/31/13 23:16, Frank Mayhar wrote:
>> On Thu, 2013-10-31 at 09:36 +0000, Junichi Nomura wrote:
>>> On 10/31/13 03:09, Frank Mayhar wrote:
>>>> On Wed, 2013-10-30 at 11:43 -0400, Mike Snitzer wrote:
>>>>> On Wed, Oct 30 2013 at 11:08am -0400,
>>>>> Frank Mayhar <fmayhar google com> wrote:
>>>>>
>>>>>> On Tue, 2013-10-29 at 21:02 -0400, Mike Snitzer wrote:
>>>>>>> Any interest in this or should I just table it for >= v3.14?
>>>>>>
>>>>>> Sorry, I've been busy putting out another fire.  Yes, there's definitely
>>>>>> still interest.  I grabbed your revised patch and tested with it.
>>>>>> Unfortunately the timeout doesn't actually fire when requests are queued
>>>>>> due to queue_if_no_path; IIRC the block request queue timeout logic
>>>>>> wasn't triggering.  I planned to look into it more deeply figure out why
>>>>>> but I had to spend all last week fixing a nasty race and hadn't gotten
>>>>>> back to it yet.
>>>>>
>>>>> OK, Hannes, any idea why this might be happening?  The patch in question
>>>>> is here: https://patchwork.kernel.org/patch/3070391/
>>>>
>>>> I got to this today and so far the most interesting I see is that the
>>>> cloned request that's queued in multipath has no queue associated with
>>>> it when it's queued; a printk reveals:
>>>>
>>>> [  517.610042] map_io: queueing rq ffff8801150e0070 q           (null)
>>>>
>>>> When it's eventually dequeued, it gets a queue from the destination
>>>> device (in the pgpath) via bdev_get_queue().
>>>>
>>>> Because of this and from just looking at the code, blk_start_request()
>>>> (and therefore blk_add_timer()) isn't being called for those requests,
>>>> so there's never a chance that the timeout would happen.
>>>>
>>>> Does this make sense?  Or am I totally off-base?
>>>
>>> Hi,
>>>
>>> I haven't checked the above patch in detail but there is a problem;
>>> abort_if_no_path() treats "rq" as a clone request, which it isn't.
>>> "rq" is an original request.
>>>
>>> It shouldn't be a correct fix but just for testing purpose, you can try
>>> changing:
>>>   info = dm_get_rq_mapinfo(rq);
>>> to
>>>   info = dm_get_rq_mapinfo(rq->special);
>>> and see what happens.
>>
>> Well, at the moment this is kind of moot since abort_if_no_path() isn't
>> being called.  But, regardless, don't we want to time out the clone
>> request?  That is, after all, what is being queued in map_io().
>> Unfortunately the clones don't appear to be associated with a request
>> queue; they're just put on multipath's internal queue.
> 
> Hmm, "isn't being called" is strange.
> If the clone is in multipath's internal queue, the original
> should have been "started" from request queue point of view
> and timeout should fire.
> 
> As for the "clone or original" question, if you are to use the block timer,
> you have to use it for the original request (then perhaps let the handler
> find its clone and kill it).
> That's because (as you already see) clones are not associated with
> request queue when it's queued in multipath internal queue
> and when it's associated, it belongs to the lower device's queue.

I slightly modified the patch:
  - fixed the timeout handler to correctly find
    clone request and "struct multipath"
  - the timeout handler just disables "queue_if_no_path"
    instead of killing the request directly
  - "dmsetup status" to show the parameter
  - changed an interface between dm core and target
  - added some debugging printk (you can remove them)
and checked the timeout occurs, at least.

I'm not sure if this feature is good or not though.
(The timer behavior is not intuitive, I think)

---
Jun'ichi Nomura, NEC Corporation


diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index 65f1035..7ea06b0 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -170,7 +170,7 @@ void blk_add_timer(struct request *req)
 	struct request_queue *q = req->q;
 	unsigned long expiry;
 
-	if (!q->rq_timed_out_fn)
+	if (!q->rq_timed_out_fn || !q->rq_timeout)
 		return;
 
 	BUG_ON(!list_empty(&req->timeout_list));
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index de570a5..c345fef 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -105,6 +105,8 @@ struct multipath {
 	mempool_t *mpio_pool;
 
 	struct mutex work_mutex;
+
+	unsigned no_path_timeout;
 };
 
 /*
@@ -444,6 +446,48 @@ static int queue_if_no_path(struct multipath *m, unsigned queue_if_no_path,
 	return 0;
 }
 
+/*
+ * Block timeout callback, called from the block layer
+ *
+ * request_queue lock is held on entry.
+ *
+ * Return values:
+ * BLK_EH_RESET_TIMER if the request should be left running
+ * BLK_EH_NOT_HANDLED if the request is handled or terminated
+ *                    by the driver.
+ */
+enum blk_eh_timer_return multipath_timed_out(struct dm_target *ti,
+					     struct request *clone)
+{
+	unsigned long flags;
+	struct multipath *m = ti->private;
+	int rc = BLK_EH_RESET_TIMER;
+	int flush_ios = 0;
+
+	printk(KERN_DEBUG "[%lu] multipath_timed_out %p %p\n", jiffies, clone, m);
+
+	/*
+	 * Only abort request if:
+	 * - queued_ios is not empty
+	 *   (protect against races with process_queued_ios)
+	 * - no valid paths are found
+	 */
+	spin_lock_irqsave(&m->lock, flags);
+	if (m->no_path_timeout &&
+	    !list_empty(&m->queued_ios) && !m->nr_valid_paths) {
+		flush_ios = 1;
+	}
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	if (flush_ios) {
+		DMWARN("disabling queue_if_no_path as I/O timed out\n");
+		queue_if_no_path(m, 0, 0);
+		queue_work(kmultipathd, &m->process_queued_ios);
+	}
+
+	return rc;
+}
+
 /*-----------------------------------------------------------------
  * The multipath daemon is responsible for resubmitting queued ios.
  *---------------------------------------------------------------*/
@@ -790,6 +834,7 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
 		{0, 6, "invalid number of feature args"},
 		{1, 50, "pg_init_retries must be between 1 and 50"},
 		{0, 60000, "pg_init_delay_msecs must be between 0 and 60000"},
+		{0, 65535, "no_path_timeout must be between 0 and 65535"},
 	};
 
 	r = dm_read_arg_group(_args, as, &argc, &ti->error);
@@ -827,6 +872,13 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
 			continue;
 		}
 
+		if (!strcasecmp(arg_name, "no_path_timeout") &&
+		    (argc >= 1)) {
+			r = dm_read_arg(_args + 3, as, &m->no_path_timeout, &ti->error);
+			argc--;
+			continue;
+		}
+
 		ti->error = "Unrecognised multipath feature request";
 		r = -EINVAL;
 	} while (argc && !r);
@@ -1384,6 +1436,9 @@ static void multipath_resume(struct dm_target *ti)
 
 	spin_lock_irqsave(&m->lock, flags);
 	m->queue_if_no_path = m->saved_queue_if_no_path;
+	if (m->no_path_timeout)
+		printk("Setting no_path_timeout %d\n", m->no_path_timeout);
+	dm_set_timeout(dm_table_get_md(m->ti->table), m->no_path_timeout);
 	spin_unlock_irqrestore(&m->lock, flags);
 }
 
@@ -1421,11 +1476,14 @@ static void multipath_status(struct dm_target *ti, status_type_t type,
 		DMEMIT("2 %u %u ", m->queue_size, m->pg_init_count);
 	else {
 		DMEMIT("%u ", m->queue_if_no_path +
+			      (m->no_path_timeout > 0) * 2 +
 			      (m->pg_init_retries > 0) * 2 +
 			      (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT) * 2 +
 			      m->retain_attached_hw_handler);
 		if (m->queue_if_no_path)
 			DMEMIT("queue_if_no_path ");
+		if (m->no_path_timeout)
+			DMEMIT("no_path_timeout %u ", m->no_path_timeout);
 		if (m->pg_init_retries)
 			DMEMIT("pg_init_retries %u ", m->pg_init_retries);
 		if (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT)
@@ -1728,6 +1786,7 @@ static struct target_type multipath_target = {
 	.ioctl  = multipath_ioctl,
 	.iterate_devices = multipath_iterate_devices,
 	.busy = multipath_busy,
+	.timed_out = multipath_timed_out,
 };
 
 static int __init dm_multipath_init(void)
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 8f87835..32c5399 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -26,6 +26,8 @@
 #define KEYS_PER_NODE (NODE_SIZE / sizeof(sector_t))
 #define CHILDREN_PER_NODE (KEYS_PER_NODE + 1)
 
+enum blk_eh_timer_return dm_rq_timed_out(struct request *rq);
+
 struct dm_table {
 	struct mapped_device *md;
 	unsigned type;
@@ -1519,6 +1521,7 @@ static void suspend_targets(struct dm_table *t, unsigned postsuspend)
 
 		ti++;
 	}
+	blk_queue_rq_timed_out(dm_disk(t->md)->queue, NULL);
 }
 
 void dm_table_presuspend_targets(struct dm_table *t)
@@ -1540,10 +1543,14 @@ void dm_table_postsuspend_targets(struct dm_table *t)
 int dm_table_resume_targets(struct dm_table *t)
 {
 	int i, r = 0;
+	int has_timeout = 0;
 
 	for (i = 0; i < t->num_targets; i++) {
 		struct dm_target *ti = t->targets + i;
 
+		if (ti->type->timed_out)
+			has_timeout = 1;
+
 		if (!ti->type->preresume)
 			continue;
 
@@ -1552,6 +1559,9 @@ int dm_table_resume_targets(struct dm_table *t)
 			return r;
 	}
 
+	if (has_timeout)
+		blk_queue_rq_timed_out(dm_disk(t->md)->queue, dm_rq_timed_out);
+
 	for (i = 0; i < t->num_targets; i++) {
 		struct dm_target *ti = t->targets + i;
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b3e26c7..701d3d2 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1026,6 +1026,13 @@ static void end_clone_request(struct request *clone, int error)
 	dm_complete_request(clone, error);
 }
 
+int dm_set_timeout(struct mapped_device *md, unsigned int tmo)
+{
+	blk_queue_rq_timeout(md->queue, tmo * HZ);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_set_timeout);
+
 /*
  * Return maximum size of I/O possible at the supplied sector up to the current
  * target boundary.
@@ -1829,6 +1836,23 @@ out:
 	dm_put_live_table(md, srcu_idx);
 }
 
+enum blk_eh_timer_return dm_rq_timed_out(struct request *rq)
+{
+	struct request *clone = rq->special;
+	struct dm_rq_target_io *tio = clone->end_io_data;
+
+	printk(KERN_DEBUG "[%lu] dm_timed_out %p : %p\n", jiffies, rq, tio);
+
+	if (!tio)
+		goto out; /* not mapped */
+
+	if (tio->ti->type->timed_out)
+		return tio->ti->type->timed_out(tio->ti, clone);
+
+out:
+	return BLK_EH_RESET_TIMER;
+}
+
 int dm_underlying_device_busy(struct request_queue *q)
 {
 	return blk_lld_busy(q);
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index ed419c6..84c0368 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -107,6 +107,8 @@ typedef int (*dm_iterate_devices_fn) (struct dm_target *ti,
 typedef void (*dm_io_hints_fn) (struct dm_target *ti,
 				struct queue_limits *limits);
 
+typedef enum blk_eh_timer_return (*dm_rq_timed_out_fn) (struct dm_target *ti,
+							struct request *clone);
 /*
  * Returns:
  *    0: The target can handle the next I/O immediately.
@@ -162,6 +164,7 @@ struct target_type {
 	dm_busy_fn busy;
 	dm_iterate_devices_fn iterate_devices;
 	dm_io_hints_fn io_hints;
+	dm_rq_timed_out_fn timed_out;
 
 	/* For internal device-mapper use. */
 	struct list_head list;
@@ -604,5 +607,6 @@ void dm_dispatch_request(struct request *rq);
 void dm_requeue_unmapped_request(struct request *rq);
 void dm_kill_unmapped_request(struct request *rq, int error);
 int dm_underlying_device_busy(struct request_queue *q);
+int dm_set_timeout(struct mapped_device *md, unsigned int tmo);
 
 #endif	/* _LINUX_DEVICE_MAPPER_H */


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