Re: Qestion about device link

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Wednesday, May 12, 2021 5:24:53 AM CEST chenxiang (M) wrote:
> Hi Rafael,
> 
> 
> 在 2021/5/12 3:16, Rafael J. Wysocki 写道:
> > 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.
> 
> I have a test on the patch, and it solves my issue.

Great, thanks!

Please also test the patch appended below (it uses a slightly different approach).

---
 drivers/base/core.c    |   37 +++++++++++++++++++++++--------------
 include/linux/device.h |    6 ++----
 2 files changed, 25 insertions(+), 18 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -193,6 +193,11 @@ int device_links_read_lock_held(void)
 {
 	return srcu_read_lock_held(&device_links_srcu);
 }
+
+void device_link_synchronize_removal(void)
+{
+	synchronize_srcu(&device_links_srcu);
+}
 #else /* !CONFIG_SRCU */
 static DECLARE_RWSEM(device_links_lock);
 
@@ -223,6 +228,10 @@ int device_links_read_lock_held(void)
 	return lockdep_is_held(&device_links_lock);
 }
 #endif
+
+static inline void device_link_synchronize_removal(void)
+{
+}
 #endif /* !CONFIG_SRCU */
 
 static bool device_is_ancestor(struct device *dev, struct device *target)
@@ -444,8 +453,13 @@ static struct attribute *devlink_attrs[]
 };
 ATTRIBUTE_GROUPS(devlink);
 
-static void device_link_free(struct device_link *link)
+static void device_link_release_fn(struct work_struct *work)
 {
+	struct device_link *link = container_of(work, struct device_link, rm_work);
+
+	/* Ensure that all references to the link object have been dropped. */
+	device_link_synchronize_removal();
+
 	while (refcount_dec_not_one(&link->rpm_active))
 		pm_runtime_put(link->supplier);
 
@@ -454,24 +468,19 @@ static void device_link_free(struct devi
 	kfree(link);
 }
 
-#ifdef CONFIG_SRCU
-static void __device_link_free_srcu(struct rcu_head *rhead)
-{
-	device_link_free(container_of(rhead, struct device_link, rcu_head));
-}
-
 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);
-}
-#else
-static void devlink_dev_release(struct device *dev)
-{
-	device_link_free(to_devlink(dev));
+	INIT_WORK(&link->rm_work, device_link_release_fn);
+	/*
+	 * It may take a while to complete this work because of the SRCU
+	 * synchronization in device_link_release_fn() and if the consumer or
+	 * supplier devices get deleted when it runs, so put it into the "long"
+	 * workqueue.
+	 */
+	queue_work(system_long_wq, &link->rm_work);
 }
-#endif
 
 static struct class devlink_class = {
 	.name = "devlink",
Index: linux-pm/include/linux/device.h
===================================================================
--- linux-pm.orig/include/linux/device.h
+++ linux-pm/include/linux/device.h
@@ -570,7 +570,7 @@ struct device {
  * @flags: Link flags.
  * @rpm_active: Whether or not the consumer device is runtime-PM-active.
  * @kref: Count repeated addition of the same link.
- * @rcu_head: An RCU head to use for deferred execution of SRCU callbacks.
+ * @rm_work: Work structure used for removing the link.
  * @supplier_preactivated: Supplier has been made active before consumer probe.
  */
 struct device_link {
@@ -583,9 +583,7 @@ struct device_link {
 	u32 flags;
 	refcount_t rpm_active;
 	struct kref kref;
-#ifdef CONFIG_SRCU
-	struct rcu_head rcu_head;
-#endif
+	struct work_struct rm_work;
 	bool supplier_preactivated; /* Owned by consumer probe. */
 };