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Subject: Re: Question about device link//Re: Qestion about device link
To:     Saravana Kannan <saravanak@google.com>,
        "chenxiang (M)" <chenxiang66@hisilicon.com>
Cc:     John Garry <john.garry@huawei.com>, linuxarm@huawei.com,
        linux-scsi@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
References: <3c88cf35-6725-1bfa-9e1e-8e9d69147e3b@hisilicon.com>
 <2e69efb9-a563-251f-2161-5546324a9587@hisilicon.com>
 <CAGETcx9FLixotMcyJmCATSoz7aB2VbYSr8o5jyM5HDd9-6LaYQ@mail.gmail.com>
From:   "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Organization: Intel Technology Poland Sp. z o. o., KRS 101882, ul. Slowackiego
 173, 80-298 Gdansk
Message-ID: <11749ea2-777c-e200-9c5a-eab531c7e69a@intel.com>
Date:   Tue, 11 May 2021 21:13:40 +0200
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On 5/11/2021 8:23 PM, Saravana Kannan wrote:
> On Tue, May 11, 2021 at 3:42 AM chenxiang (M) <chenxiang66@hisilicon.com> wrote:
>> Re-edit the non-aligned flowchart and add CC to Greg-KH and Saravanna.
>>
>>
>> 在 2021/5/11 11:59, chenxiang (M) 写道:
>>> 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()
>> Re-edit the non-aligned flowchart
>>       thread 1 thread 2
>>       hisi_sas_v3_remove()
>>               ...
>>               sas_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?
> Another report for the same issue.
> https://lore.kernel.org/lkml/CAGETcx80xSZ8d4JbZqiSz4L0VNtL+HCnFCS2u3F9aNC0QQoQjg@mail.gmail.com/
>
> I don't have enough context yet about the need for SRCU (I haven't
> read up all the runtime PM code), but this is a real issue that needs
> to be solved.
>
> Dirty/terrible hack is to kick off another work to do the
> put_device().

I wouldn't call it dirty or terrible, but it may just be the thing that 
needs to be done here.


> But is there any SRCU option that'll try to do the
> release in a non-atomic context?

No, the callbacks are run from a softirq if I'm not mistaken.

Thanks!