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From:   Saravana Kannan <saravanak@google.com>
Date:   Tue, 11 May 2021 11:23:50 -0700
Message-ID: <CAGETcx9FLixotMcyJmCATSoz7aB2VbYSr8o5jyM5HDd9-6LaYQ@mail.gmail.com>
Subject: Re: Question about device link//Re: Qestion about device link
To:     "chenxiang (M)" <chenxiang66@hisilicon.com>
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>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Tue, May 11, 2021 at 3:42 AM chenxiang (M) <chenxiang66@hisilicon.com> w=
rote:
>
> Re-edit the non-aligned flowchart and add CC to Greg-KH and Saravanna.
>
>
> =E5=9C=A8 2021/5/11 11:59, chenxiang (M) =E5=86=99=E9=81=93:
> > 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/113:1/811/0x000002=
01
> > [  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/96:1/791/0x0000020=
1
> > [  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 =3D 1)
> >                 device_link_free()
> >                               put_device(link->consumer)
> > //shost->gendev ref =3D 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 =3D 1)
>                          device_link_free()
>                                      put_device(link->consumer)
> //shost->gendev ref =3D 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 =3D0 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+HCnFCS2u3F9aNC0Q=
QoQjg@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(). But is there any SRCU option that'll try to do the
release in a non-atomic context?

-Saravana