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Message-ID: <2108146.dv4EAOf6IP@aspire.rjw.lan>
Date: Thu, 05 Jul 2018 12:11:49 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Pingfan Liu <kernelfans@...il.com>
Cc: linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Grygorii Strashko <grygorii.strashko@...com>,
Christoph Hellwig <hch@...radead.org>,
Bjorn Helgaas <helgaas@...nel.org>,
Dave Young <dyoung@...hat.com>, linux-pci@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCHv3 2/4] drivers/base: utilize device tree info to shutdown devices
On Tuesday, July 3, 2018 8:50:40 AM CEST Pingfan Liu wrote:
> commit 52cdbdd49853 ("driver core: correct device's shutdown order")
> places an assumption of supplier<-consumer order on the process of probe.
> But it turns out to break down the parent <- child order in some scene.
> E.g in pci, a bridge is enabled by pci core, and behind it, the devices
> have been probed. Then comes the bridge's module, which enables extra
> feature(such as hotplug) on this bridge. This will break the
> parent<-children order and cause failure when "kexec -e" in some scenario.
>
> The detailed description of the scenario:
> An IBM Power9 machine on which, two drivers portdrv_pci and shpchp(a mod)
> match the PCI_CLASS_BRIDGE_PCI, but neither of them success to probe due
> to some issue. For this case, the bridge is moved after its children in
> devices_kset. Then, when "kexec -e", a ata-disk behind the bridge can not
> write back buffer in flight due to the former shutdown of the bridge which
> clears the BusMaster bit.
>
> It is a little hard to impose both "parent<-child" and "supplier<-consumer"
> order on devices_kset. Take the following scene:
> step0: before a consumer's probing, (note child_a is supplier of consumer_a)
> [ consumer-X, child_a, ...., child_z] [... consumer_a, ..., consumer_z, ...] supplier-X
> ^^^^^^^^^^ affected range ^^^^^^^^^^
> step1: when probing, moving consumer-X after supplier-X
> [ child_a, ...., child_z] [.... consumer_a, ..., consumer_z, ...] supplier-X, consumer-X
> step2: the children of consumer-X should be re-ordered to maintain the seq
> [... consumer_a, ..., consumer_z, ....] supplier-X [consumer-X, child_a, ...., child_z]
> step3: the consumer_a should be re-ordered to maintain the seq
> [... consumer_z, ...] supplier-X [ consumer-X, child_a, consumer_a ..., child_z]
>
> It requires two nested recursion to drain out all out-of-order item in
> "affected range". To avoid such complicated code, this patch suggests
> to utilize the info in device tree, instead of using the order of
> devices_kset during shutdown. It iterates the device tree, and firstly
> shutdown a device's children and consumers. After this patch, the buggy
> commit is hollow and left to clean.
>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Grygorii Strashko <grygorii.strashko@...com>
> Cc: Christoph Hellwig <hch@...radead.org>
> Cc: Bjorn Helgaas <helgaas@...nel.org>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: linux-pci@...r.kernel.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> ---
> drivers/base/core.c | 48 +++++++++++++++++++++++++++++++++++++++++++-----
> include/linux/device.h | 1 +
> 2 files changed, 44 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index a48868f..684b994 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1446,6 +1446,7 @@ void device_initialize(struct device *dev)
> INIT_LIST_HEAD(&dev->links.consumers);
> INIT_LIST_HEAD(&dev->links.suppliers);
> dev->links.status = DL_DEV_NO_DRIVER;
> + dev->shutdown = false;
> }
> EXPORT_SYMBOL_GPL(device_initialize);
>
> @@ -2811,7 +2812,6 @@ static void __device_shutdown(struct device *dev)
> * lock is to be held
> */
> parent = get_device(dev->parent);
> - get_device(dev);
Why is the get_/put_device() not needed any more?
> /*
> * Make sure the device is off the kset list, in the
> * event that dev->*->shutdown() doesn't remove it.
> @@ -2842,23 +2842,60 @@ static void __device_shutdown(struct device *dev)
> dev_info(dev, "shutdown\n");
> dev->driver->shutdown(dev);
> }
> -
> + dev->shutdown = true;
> device_unlock(dev);
> if (parent)
> device_unlock(parent);
>
> - put_device(dev);
> put_device(parent);
> spin_lock(&devices_kset->list_lock);
> }
>
> +/* shutdown dev's children and consumer firstly, then itself */
> +static int device_for_each_child_shutdown(struct device *dev)
Confusing name.
What about device_shutdown_subordinate()?
> +{
> + struct klist_iter i;
> + struct device *child;
> + struct device_link *link;
> +
> + /* already shutdown, then skip this sub tree */
> + if (dev->shutdown)
> + return 0;
> +
> + if (!dev->p)
> + goto check_consumers;
> +
> + /* there is breakage of lock in __device_shutdown(), and the redundant
> + * ref++ on srcu protected consumer is harmless since shutdown is not
> + * hot path.
> + */
> + get_device(dev);
> +
> + klist_iter_init(&dev->p->klist_children, &i);
> + while ((child = next_device(&i)))
> + device_for_each_child_shutdown(child);
Why don't you use device_for_each_child() here?
> + klist_iter_exit(&i);
> +
> +check_consumers:
> + list_for_each_entry_rcu(link, &dev->links.consumers, s_node) {
> + if (!link->consumer->shutdown)
> + device_for_each_child_shutdown(link->consumer);
> + }
> +
> + __device_shutdown(dev);
> + put_device(dev);
Possible reference counter imbalance AFAICS.
> + return 0;
> +}
Well, instead of doing this dance, we might as well walk dpm_list here as it
is in the right order.
Of course, that would require dpm_list to be available for CONFIG_PM unset,
but it may be a better approach long term.
> +
> /**
> * device_shutdown - call ->shutdown() on each device to shutdown.
> */
> void device_shutdown(void)
> {
> struct device *dev;
> + int idx;
>
> + idx = device_links_read_lock();
> spin_lock(&devices_kset->list_lock);
> /*
> * Walk the devices list backward, shutting down each in turn.
> @@ -2866,11 +2903,12 @@ void device_shutdown(void)
> * devices offline, even as the system is shutting down.
> */
> while (!list_empty(&devices_kset->list)) {
> - dev = list_entry(devices_kset->list.prev, struct device,
> + dev = list_entry(devices_kset->list.next, struct device,
> kobj.entry);
> - __device_shutdown(dev);
> + device_for_each_child_shutdown(dev);
> }
> spin_unlock(&devices_kset->list_lock);
> + device_links_read_unlock(idx);
> }
>
> /*
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 055a69d..8a0f784 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1003,6 +1003,7 @@ struct device {
> bool offline:1;
> bool of_node_reused:1;
> bool dma_32bit_limit:1;
> + bool shutdown:1; /* one direction: false->true */
> };
>
> static inline struct device *kobj_to_dev(struct kobject *kobj)
>
If the device_kset_move_last() in really_probe() is the only problem,
I'd rather try to fix that one in the first place.
Why is it needed?
Thanks,
Rafael
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