Re: Question about device link//Re: Qestion about device link

From: Saravana Kannan
Date: Tue May 11 2021 - 14:24:33 EST

On Tue, May 11, 2021 at 3:42 AM chenxiang (M) <chenxiang66@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx/

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