Re: Qestion about device link
From: chenxiang (M)
Date: Wed May 12 2021 - 23:00:53 EST
Hi Rafael,
在 2021/5/12 22:04, Rafael J. Wysocki 写道:
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).
I have a test on this change, and it also solves my issue.
---
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. */
};
.