Re: Qestion about device link

From: Rafael J. Wysocki
Date: Tue May 11 2021 - 15:16:59 EST

On Tuesday, May 11, 2021 4:39:31 PM CEST Rafael J. Wysocki wrote:
> 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.

Please test the patch below and let me know if it works for you.

---
drivers/base/core.c | 18 ++++++++++++++++--
include/linux/device.h | 5 ++++-
2 files changed, 20 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -455,16 +455,30 @@ static void device_link_free(struct devi
}

#ifdef CONFIG_SRCU
+static void __device_link_free_fn(struct work_struct *work)
+{
+ device_link_free(container_of(work, struct device_link, srcu.work));
+}
+
static void __device_link_free_srcu(struct rcu_head *rhead)
{
- device_link_free(container_of(rhead, struct device_link, rcu_head));
+ struct device_link *link = container_of(rhead, struct device_link,
+ srcu.rhead);
+ struct work_struct *work = &link->srcu.work;
+
+ /*
+ * Because device_link_free() may sleep in some cases, schedule the
+ * execution of it instead of invoking it directly.
+ */
+ INIT_WORK(work, __device_link_free_fn);
+ schedule_work(work);
}

static void devlink_dev_release(struct device *dev)
{
struct device_link *link = to_devlink(dev);

- call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
+ call_srcu(&device_links_srcu, &link->srcu.rhead, __device_link_free_srcu);
}
#else
static void devlink_dev_release(struct device *dev)
Index: linux-pm/include/linux/device.h
===================================================================
--- linux-pm.orig/include/linux/device.h
+++ linux-pm/include/linux/device.h
@@ -584,7 +584,10 @@ struct device_link {
refcount_t rpm_active;
struct kref kref;
#ifdef CONFIG_SRCU
- struct rcu_head rcu_head;
+ union {
+ struct rcu_head rhead;
+ struct work_struct work;
+ } srcu;
#endif
bool supplier_preactivated; /* Owned by consumer probe. */
};