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Subject: Re: Qestion about device link
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
References: <3c88cf35-6725-1bfa-9e1e-8e9d69147e3b@hisilicon.com>
 <d16058fc-9876-f6a3-d5e8-ff06b5193f2c@intel.com>
 <2149723.iZASKD2KPV@kreacher>
CC:     "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        John Garry <john.garry@huawei.com>, <linuxarm@huawei.com>,
        <linux-scsi@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Saravana Kannan <saravanak@google.com>
From:   "chenxiang (M)" <chenxiang66@hisilicon.com>
Message-ID: <1c1cd889-7e6f-79f7-2650-cd181abc56b2@hisilicon.com>
Date:   Wed, 12 May 2021 11:24:53 +0800
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Hi Rafael,


在 2021/5/12 3:16, Rafael J. Wysocki 写道:
> On Tuesday, May 11, 2021 4:39:31 PM CEST Rafael J. Wysocki wrote:
>> On 5/11/2021 5:59 AM, chenxiang (M) wrote:
>>> Hi Rafael and other guys,
>>>
>>> I am trying to add a device link between scsi_host->shost_gendev and
>>> hisi_hba->dev to support runtime PM for hisi_hba driver
>>>
>>> (as it supports runtime PM for scsi host in some scenarios such as
>>> error handler etc, we can avoid to do them again if adding a
>>>
>>> device link between scsi_host->shost_gendev and hisi_hba->dev) as
>>> follows (hisi_sas driver is under directory drivers/scsi/hisi_sas):
>>>
>>> device_link_add(&shost->shost_gendev, hisi_hba->dev,
>>> DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE)
>>>
>>> We have a full test on it, and it works well except when rmmod the
>>> driver, some call trace occurs as follows:
>>>
>>> [root@localhost ~]# rmmod hisi_sas_v3_hw
>>> [  105.377944] BUG: scheduling while atomic: kworker/113:1/811/0x00000201
>>> [  105.384469] Modules linked in: bluetooth rfkill ib_isert
>>> iscsi_target_mod ib_ipoib ib_umad iptable_filter vfio_iommu_type1
>>> vfio_pci vfio_virqfd vfio rpcrdma ib_is                         er
>>> libiscsi scsi_transport_iscsi crct10dif_ce sbsa_gwdt hns_roce_hw_v2
>>> hisi_sec2 hisi_hpre hisi_zip hisi_qm uacce spi_hisi_sfc_v3xx
>>> hisi_trng_v2 rng_core hisi_uncore                         _hha_pmu
>>> hisi_uncore_ddrc_pmu hisi_uncore_l3c_pmu spi_dw_mmio hisi_uncore_pmu
>>> hns3 hclge hnae3 hisi_sas_v3_hw(-) hisi_sas_main libsas
>>> [  105.424841] CPU: 113 PID: 811 Comm: kworker/113:1 Kdump: loaded
>>> Tainted: G        W         5.12.0-rc1+ #1
>>> [  105.434454] Hardware name: Huawei TaiShan 2280 V2/BC82AMDC, BIOS
>>> 2280-V2 CS V5.B143.01 04/22/2021
>>> [  105.443287] Workqueue: rcu_gp srcu_invoke_callbacks
>>> [  105.448154] Call trace:
>>> [  105.450593]  dump_backtrace+0x0/0x1a4
>>> [  105.454245]  show_stack+0x24/0x40
>>> [  105.457548]  dump_stack+0xc8/0x104
>>> [  105.460939]  __schedule_bug+0x68/0x80
>>> [  105.464590]  __schedule+0x73c/0x77c
>>> [  105.465700] BUG: scheduling while atomic: kworker/96:1/791/0x00000201
>>> [  105.468066]  schedule+0x7c/0x110
>>> [  105.468068]  schedule_timeout+0x194/0x1d4
>>> [  105.474490] Modules linked in:
>>> [  105.477692]  wait_for_completion+0x8c/0x12c
>>> [  105.477695]  rcu_barrier+0x1e0/0x2fc
>>> [  105.477697]  scsi_host_dev_release+0x50/0xf0
>>> [  105.477701]  device_release+0x40/0xa0
>>> [  105.477704]  kobject_put+0xac/0x100
>>> [  105.477707]  __device_link_free_srcu+0x50/0x74
>>> [  105.477709]  srcu_invoke_callbacks+0x108/0x1a4
>>> [  105.484743]  process_one_work+0x1dc/0x48c
>>> [  105.492468]  worker_thread+0x7c/0x464
>>> [  105.492471]  kthread+0x168/0x16c
>>> [  105.492473]  ret_from_fork+0x10/0x18
>>> ...
>>>
>>> After analyse the process, we find that it will
>>> device_del(&shost->gendev) in function scsi_remove_host() and then
>>>
>>> put_device(&shost->shost_gendev) in function scsi_host_put() when
>>> removing the driver, if there is a link between shost and hisi_hba->dev,
>>>
>>> it will try to delete the link in device_del(), and also will
>>> call_srcu(__device_link_free_srcu) to put_device() link->consumer and
>>> supplier.
>>>
>>> But if put device() for shost_gendev in device_link_free() is later
>>> than in scsi_host_put(), it will call scsi_host_dev_release() in
>>>
>>> srcu_invoke_callbacks() while it is atomic and there are scheduling in
>>> scsi_host_dev_release(),
>>>
>>> so it reports the BUG "scheduling while atomic:...".
>>>
>>> thread 1                                                   thread2
>>> hisi_sas_v3_remove
>>>      ...
>>>      sas_remove_host()
>>>          ...
>>>          scsi_remove_host()
>>>              ...
>>>              device_del(&shost->shost_gendev)
>>>                  ...
>>>                  device_link_purge()
>>>                      __device_link_del()
>>>                          device_unregister(&link->link_dev)
>>>                              devlink_dev_release
>>> call_srcu(__device_link_free_srcu)    ----------->
>>> srcu_invoke_callbacks  (atomic)
>>>          __device_link_free_srcu
>>>      ...
>>>      scsi_host_put()
>>>          put_device(&shost->shost_gendev) (ref = 1)
>>>                  device_link_free()
>>>                                put_device(link->consumer)
>>> //shost->gendev ref = 0
>>>                                            ...
>>>                                            scsi_host_dev_release
>>>                                                        ...
>>> rcu_barrier
>>> kthread_stop()
>>>
>>>
>>> We can check kref of shost->shost_gendev to make sure scsi_host_put()
>>> to release scsi host device in LLDD driver to avoid the issue,
>>>
>>> but it seems be a common issue:  function __device_link_free_srcu
>>> calls put_device() for consumer and supplier,
>>>
>>> but if it's ref =0 at that time and there are scheduling or sleep in
>>> dev_release, it may have the issue.
>>>
>>> Do you have any idea about the issue?
>>>
>> Yes, this is a general issue.
>>
>> If I'm not mistaken, it can be addressed by further deferring the
>> device_link_free() invocation through a workqueue.
>>
>> Let me cut a patch doing this.
> Please test the patch below and let me know if it works for you.

I have a test on the patch, and it solves my issue.


>
> ---
>   drivers/base/core.c    |   18 ++++++++++++++++--
>   include/linux/device.h |    5 ++++-
>   2 files changed, 20 insertions(+), 3 deletions(-)
>
> Index: linux-pm/drivers/base/core.c
> ===================================================================
> --- linux-pm.orig/drivers/base/core.c
> +++ linux-pm/drivers/base/core.c
> @@ -455,16 +455,30 @@ static void device_link_free(struct devi
>   }
>   
>   #ifdef CONFIG_SRCU
> +static void __device_link_free_fn(struct work_struct *work)
> +{
> +	device_link_free(container_of(work, struct device_link, srcu.work));
> +}
> +
>   static void __device_link_free_srcu(struct rcu_head *rhead)
>   {
> -	device_link_free(container_of(rhead, struct device_link, rcu_head));
> +	struct device_link *link = container_of(rhead, struct device_link,
> +						srcu.rhead);
> +	struct work_struct *work = &link->srcu.work;
> +
> +	/*
> +	 * Because device_link_free() may sleep in some cases, schedule the
> +	 * execution of it instead of invoking it directly.
> +	 */
> +	INIT_WORK(work, __device_link_free_fn);
> +	schedule_work(work);
>   }
>   
>   static void devlink_dev_release(struct device *dev)
>   {
>   	struct device_link *link = to_devlink(dev);
>   
> -	call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
> +	call_srcu(&device_links_srcu, &link->srcu.rhead, __device_link_free_srcu);
>   }
>   #else
>   static void devlink_dev_release(struct device *dev)
> Index: linux-pm/include/linux/device.h
> ===================================================================
> --- linux-pm.orig/include/linux/device.h
> +++ linux-pm/include/linux/device.h
> @@ -584,7 +584,10 @@ struct device_link {
>   	refcount_t rpm_active;
>   	struct kref kref;
>   #ifdef CONFIG_SRCU
> -	struct rcu_head rcu_head;
> +	union {
> +		struct rcu_head rhead;
> +		struct work_struct work;
> +	} srcu;
>   #endif
>   	bool supplier_preactivated; /* Owned by consumer probe. */
>   };
>
>
>
>
> .
>