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From: Ming Lei <ming.lei@redhat.com>
To: Daniel Wagner <dwagner@suse.de>
Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
	James Smart <james.smart@broadcom.com>,
	Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>,
	Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [PATCH 2/2] nvme-fc: Wait with a timeout for queue to freeze
Date: Tue, 6 Jul 2021 15:29:11 +0800	[thread overview]
Message-ID: <YOQGRwLfLaFGqlVA@T590> (raw)
In-Reply-To: <20210705162519.qqlklisxcsiopflw@beryllium.lan>

On Mon, Jul 05, 2021 at 06:34:00PM +0200, Daniel Wagner wrote:
> On Tue, Jun 29, 2021 at 09:39:30AM +0800, Ming Lei wrote:
> > Can you investigate a bit on why there is the hang? FC shouldn't use
> > managed IRQ, so the interrupt won't be shutdown.
> 
> So far, I was not able to figure out why this hangs. In my test setup I
> don't have to do any I/O, I just toggle the remote port.
> 
>   grep busy /sys/kernel/debug/block/*/hctx*/tags | grep -v busy=0
> 
> and this seems to confirm, no I/O in flight.

What is the output of the following command after the hang is triggered?

(cd /sys/kernel/debug/block/nvme0n1 && find . -type f -exec grep -aH . {} \;)

Suppose the hang disk is nvme0n1.

> 
> So I started to look at the q_usage_counter. The obvious observational
> is that counter is not 0. The least bit is set, thus we are in atomic
> mode. 
> 
> (gdb) p/x *((struct request_queue*)0xffff8ac992fbef20)->q_usage_counter->data
> $10 = {
>   count = {
>     counter = 0x8000000000000001
>   }, 
>   release = 0xffffffffa02e78b0, 
>   confirm_switch = 0x0, 
>   force_atomic = 0x0, 
>   allow_reinit = 0x1, 
>   rcu = {
>     next = 0x0, 
>     func = 0x0
>   }, 
>   ref = 0xffff8ac992fbef30
> }
> 
> I am a bit confused about the percpu-refcount API. My naive
> interpretation is that when we are in atomic mode percpu_ref_is_zero()
> can't be used. But this seems rather strange. I must miss something.

No, percpu_ref_is_zero() is fine to be called in atomic mode.


Thanks,
Ming


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Linux-nvme@lists.infradead.org
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WARNING: multiple messages have this Message-ID (diff)
From: Ming Lei <ming.lei@redhat.com>
To: Daniel Wagner <dwagner@suse.de>
Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
	James Smart <james.smart@broadcom.com>,
	Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>,
	Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [PATCH 2/2] nvme-fc: Wait with a timeout for queue to freeze
Date: Tue, 6 Jul 2021 15:29:11 +0800	[thread overview]
Message-ID: <YOQGRwLfLaFGqlVA@T590> (raw)
In-Reply-To: <20210705162519.qqlklisxcsiopflw@beryllium.lan>

On Mon, Jul 05, 2021 at 06:34:00PM +0200, Daniel Wagner wrote:
> On Tue, Jun 29, 2021 at 09:39:30AM +0800, Ming Lei wrote:
> > Can you investigate a bit on why there is the hang? FC shouldn't use
> > managed IRQ, so the interrupt won't be shutdown.
> 
> So far, I was not able to figure out why this hangs. In my test setup I
> don't have to do any I/O, I just toggle the remote port.
> 
>   grep busy /sys/kernel/debug/block/*/hctx*/tags | grep -v busy=0
> 
> and this seems to confirm, no I/O in flight.

What is the output of the following command after the hang is triggered?

(cd /sys/kernel/debug/block/nvme0n1 && find . -type f -exec grep -aH . {} \;)

Suppose the hang disk is nvme0n1.

> 
> So I started to look at the q_usage_counter. The obvious observational
> is that counter is not 0. The least bit is set, thus we are in atomic
> mode. 
> 
> (gdb) p/x *((struct request_queue*)0xffff8ac992fbef20)->q_usage_counter->data
> $10 = {
>   count = {
>     counter = 0x8000000000000001
>   }, 
>   release = 0xffffffffa02e78b0, 
>   confirm_switch = 0x0, 
>   force_atomic = 0x0, 
>   allow_reinit = 0x1, 
>   rcu = {
>     next = 0x0, 
>     func = 0x0
>   }, 
>   ref = 0xffff8ac992fbef30
> }
> 
> I am a bit confused about the percpu-refcount API. My naive
> interpretation is that when we are in atomic mode percpu_ref_is_zero()
> can't be used. But this seems rather strange. I must miss something.

No, percpu_ref_is_zero() is fine to be called in atomic mode.


Thanks,
Ming


  reply	other threads:[~2021-07-06  7:29 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-25 10:16 [PATCH 0/2] Handle update hardware queues and queue freeze more carefully Daniel Wagner
2021-06-25 10:16 ` Daniel Wagner
2021-06-25 10:16 ` [PATCH 1/2] nvme-fc: Update hardware queues before using them Daniel Wagner
2021-06-25 10:16   ` Daniel Wagner
2021-06-27 13:47   ` James Smart
2021-06-27 13:47     ` James Smart
2021-06-29  1:32   ` Ming Lei
2021-06-29  1:32     ` Ming Lei
2021-06-29 12:31   ` Hannes Reinecke
2021-06-29 12:31     ` Hannes Reinecke
2021-06-25 10:16 ` [PATCH 2/2] nvme-fc: Wait with a timeout for queue to freeze Daniel Wagner
2021-06-25 10:16   ` Daniel Wagner
2021-06-27 14:04   ` James Smart
2021-06-27 14:04     ` James Smart
2021-06-29  1:39   ` Ming Lei
2021-06-29  1:39     ` Ming Lei
2021-06-29  7:48     ` Daniel Wagner
2021-06-29  7:48       ` Daniel Wagner
2021-07-05 16:34     ` Daniel Wagner
2021-07-05 16:34       ` Daniel Wagner
2021-07-06  7:29       ` Ming Lei [this message]
2021-07-06  7:29         ` Ming Lei
2021-07-06  8:10         ` Daniel Wagner
2021-07-06  8:10           ` Daniel Wagner
2021-07-06  8:45           ` Ming Lei
2021-07-06  8:45             ` Ming Lei
2021-07-06  8:59             ` Daniel Wagner
2021-07-06  8:59               ` Daniel Wagner
2021-07-06 12:21               ` Daniel Wagner
2021-07-06 12:21                 ` Daniel Wagner
2021-07-07  2:46                 ` Ming Lei
2021-07-07  2:46                   ` Ming Lei
2021-06-29 12:31   ` Hannes Reinecke
2021-06-29 12:31     ` Hannes Reinecke
2021-06-25 12:21 ` [PATCH 0/2] Handle update hardware queues and queue freeze more carefully Daniel Wagner
2021-06-25 12:21   ` Daniel Wagner
2021-06-25 13:00   ` Ming Lei
2021-06-25 13:00     ` Ming Lei
2021-06-29  1:31     ` Ming Lei
2021-06-29  1:31       ` Ming Lei

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