thr3ads.net - Virtualization - 4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk (also 4.12 stable) [Nov 2017]

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Jens Axboe

2017-Nov-21 18:27 UTC

4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk (also 4.12 stable)

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 at lst.de>
>>>> 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 at lst.de>
>>>>     Reviewed-by: Jens Axboe <axboe at kernel.dk>
>>>>     Cc: Keith Busch <keith.busch at intel.com>
>>>>     Cc: linux-block at vger.kernel.org
>>>>     Cc: linux-nvme at lists.infradead.org
>>>>     Link: http://lkml.kernel.org/r/20170626102058.10200-3-hch
at lst.de
>>>>     Signed-off-by: Thomas Gleixner <tglx at
linutronix.de>
>>>>     Cc: Oleksandr Natalenko <oleksandr at natalenko.name>
>>>>     Cc: Mike Galbraith <efault at gmx.de>
>>>>     Signed-off-by: Greg Kroah-Hartman <gregkh at
linuxfoundation.org>
>>>
>>> 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.

-- 
Jens Axboe

Jens Axboe

2017-Nov-21 18:39 UTC

head link

4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk (also 4.12 stable)

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 at lst.de>
>>>>> 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 at lst.de>
>>>>>     Reviewed-by: Jens Axboe <axboe at kernel.dk>
>>>>>     Cc: Keith Busch <keith.busch at intel.com>
>>>>>     Cc: linux-block at vger.kernel.org
>>>>>     Cc: linux-nvme at lists.infradead.org
>>>>>     Link:
http://lkml.kernel.org/r/20170626102058.10200-3-hch at lst.de
>>>>>     Signed-off-by: Thomas Gleixner <tglx at
linutronix.de>
>>>>>     Cc: Oleksandr Natalenko <oleksandr at
natalenko.name>
>>>>>     Cc: Mike Galbraith <efault at gmx.de>
>>>>>     Signed-off-by: Greg Kroah-Hartman <gregkh at
linuxfoundation.org>
>>>>
>>>> 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?


diff --git a/block/blk-mq.c b/block/blk-mq.c
index b600463791ec..ab3a66e7bd03 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -40,6 +40,7 @@
 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);
+static void blk_mq_map_swqueue(struct request_queue *q);
 
 static int blk_mq_poll_stats_bkt(const struct request *rq)
 {
@@ -1947,6 +1950,15 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set, struct
blk_mq_tags *tags,
 	return -ENOMEM;
 }
 
+static int blk_mq_hctx_notify_prepare(unsigned int cpu, struct hlist_node
*node)
+{
+	struct blk_mq_hw_ctx *hctx;
+
+	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp);
+	blk_mq_map_swqueue(hctx->queue);
+	return 0;
+}
+
 /*
  * 'cpu' is going away. splice any existing rq_list entries from this
  * software queue to the hw queue dispatch list, and ensure that it
@@ -1958,7 +1970,7 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu,
struct hlist_node *node)
 	struct blk_mq_ctx *ctx;
 	LIST_HEAD(tmp);
 
-	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp_dead);
+	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp);
 	ctx = __blk_mq_get_ctx(hctx->queue, cpu);
 
 	spin_lock(&ctx->lock);
@@ -1981,8 +1993,7 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu,
struct hlist_node *node)
 
 static void blk_mq_remove_cpuhp(struct blk_mq_hw_ctx *hctx)
 {
-	cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_DEAD,
-					    &hctx->cpuhp_dead);
+	cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_PREPARE,
&hctx->cpuhp);
 }
 
 /* hctx->ctxs will be freed in queue's release handler */
@@ -2039,7 +2050,7 @@ static int blk_mq_init_hctx(struct request_queue *q,
 	hctx->queue = q;
 	hctx->flags = set->flags & ~BLK_MQ_F_TAG_SHARED;
 
-	cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_DEAD, &hctx->cpuhp_dead);
+	cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_PREPARE, &hctx->cpuhp);
 
 	hctx->tags = set->tags[hctx_idx];
 
@@ -2974,7 +2987,8 @@ static int __init blk_mq_init(void)
 	BUILD_BUG_ON((REQ_ATOM_STARTED / BITS_PER_BYTE) ! 			(REQ_ATOM_COMPLETE /
BITS_PER_BYTE));
 
-	cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL,
+	cpuhp_setup_state_multi(CPUHP_BLK_MQ_PREPARE, "block/mq:prepare",
+				blk_mq_hctx_notify_prepare,
 				blk_mq_hctx_notify_dead);
 	return 0;
 }
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 95c9a5c862e2..a6f03e9464fb 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -52,7 +52,7 @@ struct blk_mq_hw_ctx {
 
 	atomic_t		nr_active;
 
-	struct hlist_node	cpuhp_dead;
+	struct hlist_node	cpuhp;
 	struct kobject		kobj;
 
 	unsigned long		poll_considered;
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index ec32c4c5eb30..28b0fc9229c8 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -48,7 +48,7 @@ enum cpuhp_state {
 	CPUHP_BLOCK_SOFTIRQ_DEAD,
 	CPUHP_ACPI_CPUDRV_DEAD,
 	CPUHP_S390_PFAULT_DEAD,
-	CPUHP_BLK_MQ_DEAD,
+	CPUHP_BLK_MQ_PREPARE,
 	CPUHP_FS_BUFF_DEAD,
 	CPUHP_PRINTK_DEAD,
 	CPUHP_MM_MEMCQ_DEAD,

-- 
Jens Axboe

Christian Borntraeger

2017-Nov-21 19:15 UTC

head link

4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk (also 4.12 stable)

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 at lst.de>
>>>>>> 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 at
lst.de>
>>>>>>     Reviewed-by: Jens Axboe <axboe at kernel.dk>
>>>>>>     Cc: Keith Busch <keith.busch at intel.com>
>>>>>>     Cc: linux-block at vger.kernel.org
>>>>>>     Cc: linux-nvme at lists.infradead.org
>>>>>>     Link:
http://lkml.kernel.org/r/20170626102058.10200-3-hch at lst.de
>>>>>>     Signed-off-by: Thomas Gleixner <tglx at
linutronix.de>
>>>>>>     Cc: Oleksandr Natalenko <oleksandr at
natalenko.name>
>>>>>>     Cc: Mike Galbraith <efault at gmx.de>
>>>>>>     Signed-off-by: Greg Kroah-Hartman <gregkh at
linuxfoundation.org>
>>>>>
>>>>> 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
> 
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index b600463791ec..ab3a66e7bd03 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -40,6 +40,7 @@
>  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);
> +static void blk_mq_map_swqueue(struct request_queue *q);
> 
>  static int blk_mq_poll_stats_bkt(const struct request *rq)
>  {
> @@ -1947,6 +1950,15 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set,
struct blk_mq_tags *tags,
>  	return -ENOMEM;
>  }
> 
> +static int blk_mq_hctx_notify_prepare(unsigned int cpu, struct hlist_node
*node)
> +{
> +	struct blk_mq_hw_ctx *hctx;
> +
> +	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp);
> +	blk_mq_map_swqueue(hctx->queue);
> +	return 0;
> +}
> +
>  /*
>   * 'cpu' is going away. splice any existing rq_list entries from
this
>   * software queue to the hw queue dispatch list, and ensure that it
> @@ -1958,7 +1970,7 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu,
struct hlist_node *node)
>  	struct blk_mq_ctx *ctx;
>  	LIST_HEAD(tmp);
> 
> -	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp_dead);
> +	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp);
>  	ctx = __blk_mq_get_ctx(hctx->queue, cpu);
> 
>  	spin_lock(&ctx->lock);
> @@ -1981,8 +1993,7 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu,
struct hlist_node *node)
> 
>  static void blk_mq_remove_cpuhp(struct blk_mq_hw_ctx *hctx)
>  {
> -	cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_DEAD,
> -					    &hctx->cpuhp_dead);
> +	cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_PREPARE,
&hctx->cpuhp);
>  }
> 
>  /* hctx->ctxs will be freed in queue's release handler */
> @@ -2039,7 +2050,7 @@ static int blk_mq_init_hctx(struct request_queue *q,
>  	hctx->queue = q;
>  	hctx->flags = set->flags & ~BLK_MQ_F_TAG_SHARED;
> 
> -	cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_DEAD,
&hctx->cpuhp_dead);
> +	cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_PREPARE,
&hctx->cpuhp);
> 
>  	hctx->tags = set->tags[hctx_idx];
> 
> @@ -2974,7 +2987,8 @@ static int __init blk_mq_init(void)
>  	BUILD_BUG_ON((REQ_ATOM_STARTED / BITS_PER_BYTE) !>  		
(REQ_ATOM_COMPLETE / BITS_PER_BYTE));
> 
> -	cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead",
NULL,
> +	cpuhp_setup_state_multi(CPUHP_BLK_MQ_PREPARE,
"block/mq:prepare",
> +				blk_mq_hctx_notify_prepare,
>  				blk_mq_hctx_notify_dead);
>  	return 0;
>  }
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 95c9a5c862e2..a6f03e9464fb 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -52,7 +52,7 @@ struct blk_mq_hw_ctx {
> 
>  	atomic_t		nr_active;
> 
> -	struct hlist_node	cpuhp_dead;
> +	struct hlist_node	cpuhp;
>  	struct kobject		kobj;
> 
>  	unsigned long		poll_considered;
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index ec32c4c5eb30..28b0fc9229c8 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -48,7 +48,7 @@ enum cpuhp_state {
>  	CPUHP_BLOCK_SOFTIRQ_DEAD,
>  	CPUHP_ACPI_CPUDRV_DEAD,
>  	CPUHP_S390_PFAULT_DEAD,
> -	CPUHP_BLK_MQ_DEAD,
> +	CPUHP_BLK_MQ_PREPARE,
>  	CPUHP_FS_BUFF_DEAD,
>  	CPUHP_PRINTK_DEAD,
>  	CPUHP_MM_MEMCQ_DEAD,
>

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