Re: Qestion about device link

From: Rafael J. Wysocki
Date: Tue May 11 2021 - 10:39:44 EST

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
call_srcu(__device_link_free_srcu)    -----------> srcu_invoke_callbacks  (atomic)
        put_device(&shost->shost_gendev) (ref = 1)
                              put_device(link->consumer) //shost->gendev ref = 0

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.