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Message-ID: <CAGETcx_RpAt8j9y5PPKhkfNAzV1--pC5=4rvcLx6Lp3FgP90Ng@mail.gmail.com>
Date: Thu, 13 May 2021 09:43:19 -0700
From: Saravana Kannan <saravanak@...gle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
"chenxiang (M)" <chenxiang66@...ilicon.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
John Garry <john.garry@...wei.com>,
Linuxarm <linuxarm@...wei.com>,
"open list:TARGET SUBSYSTEM" <linux-scsi@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Linux PM <linux-pm@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Qestion about device link
On Thu, May 13, 2021 at 5:13 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, May 13, 2021 at 12:24 AM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > On Wed, May 12, 2021 at 7:04 AM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > >
> > > 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@...alhost ~]# 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);
> >
> > Not too strong of an opinion, but this seems like an unnecessary work
> > queue when SRCUs aren't enabled.
>
> It is not strictly necessary then, but I want the code with and
> without SRCU to be as similar as possible and it doesn't really hurt
> to defer the freeing of memory associated with the device link even in
> the non-SRCU case, because whoever drops the last reference to the
> device link doesn't really care when that memory gets released and may
> not want to wait until that actually happens.
Yeah, I fully understand why you did it. I was just wondering if it
was worth the additional CPU cycles and context switching. I'll leave
it at that.
Whichever way you go:
Reviewed-by: Saravana Kannan <saravanak@...gle.com>
-Saravana
>
> > We could just leave this part as is and limit your changes to the SRCU implementation?
>
> I don't really see why that would be better.
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