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Subject: Re: Qestion about device link
To:     "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>,
        Linux PM <linux-pm@vger.kernel.org>
References: <3c88cf35-6725-1bfa-9e1e-8e9d69147e3b@hisilicon.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: <d16058fc-9876-f6a3-d5e8-ff06b5193f2c@intel.com>
Date:   Tue, 11 May 2021 16:39:31 +0200
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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.