From: Jiang Liu <liuj97@gmail.com>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Toshi Kani <toshi.kani@hp.com>,
linux-acpi@vger.kernel.org, Hanjun Guo <guohanjun@huawei.com>,
Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>,
isimatu.yasuaki@jp.fujitsu.com, wency@cn.fujitsu.com,
lenb@kernel.org, gregkh@linuxfoundation.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Tang Chen <tangchen@cn.fujitsu.com>
Subject: Re: [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation
Date: Fri, 07 Dec 2012 01:07:09 +0800 [thread overview]
Message-ID: <50C0D0BD.9060901@gmail.com> (raw)
In-Reply-To: <1553400.FCdSlj7sbe@vostro.rjw.lan>
On 11/30/2012 04:30 AM, Rafael J. Wysocki wrote:
> On Thursday, November 29, 2012 10:03:12 AM Toshi Kani wrote:
>> On Thu, 2012-11-29 at 11:15 +0100, Rafael J. Wysocki wrote:
>>> On Wednesday, November 28, 2012 11:41:36 AM Toshi Kani wrote:
>>>> On Wed, 2012-11-28 at 19:05 +0800, Hanjun Guo wrote:
>>>>> On 2012/11/24 1:50, Vasilis Liaskovitis wrote:
>>>>>> As discussed in https://patchwork.kernel.org/patch/1581581/
>>>>>> the driver core remove function needs to always succeed. This means we need
>>>>>> to know that the device can be successfully removed before acpi_bus_trim /
>>>>>> acpi_bus_hot_remove_device are called. This can cause panics when OSPM-initiated
>>>>>> or SCI-initiated eject of memory devices fail e.g with:
>>>>>> echo 1 >/sys/bus/pci/devices/PNP0C80:XX/eject
>>>>>>
>>>>>> since the ACPI core goes ahead and ejects the device regardless of whether the
>>>>>> the memory is still in use or not.
>>>>>>
>>>>>> For this reason a new acpi_device operation called prepare_remove is introduced.
>>>>>> This operation should be registered for acpi devices whose removal (from kernel
>>>>>> perspective) can fail. Memory devices fall in this category.
>>>>>>
>>>>>> acpi_bus_remove() is changed to handle removal in 2 steps:
>>>>>> - preparation for removal i.e. perform part of removal that can fail. Should
>>>>>> succeed for device and all its children.
>>>>>> - if above step was successfull, proceed to actual device removal
>>>>>
>>>>> Hi Vasilis,
>>>>> We met the same problem when we doing computer node hotplug, It is a good idea
>>>>> to introduce prepare_remove before actual device removal.
>>>>>
>>>>> I think we could do more in prepare_remove, such as rollback. In most cases, we can
>>>>> offline most of memory sections except kernel used pages now, should we rollback
>>>>> and online the memory sections when prepare_remove failed ?
>>>>
>>>> I think hot-plug operation should have all-or-nothing semantics. That
>>>> is, an operation should either complete successfully, or rollback to the
>>>> original state.
>>>
>>> That's correct.
>>>
>>>>> As you may know, the ACPI based hotplug framework we are working on already addressed
>>>>> this problem, and the way we slove this problem is a bit like yours.
>>>>>
>>>>> We introduce hp_ops in struct acpi_device_ops:
>>>>> struct acpi_device_ops {
>>>>> acpi_op_add add;
>>>>> acpi_op_remove remove;
>>>>> acpi_op_start start;
>>>>> acpi_op_bind bind;
>>>>> acpi_op_unbind unbind;
>>>>> acpi_op_notify notify;
>>>>> #ifdef CONFIG_ACPI_HOTPLUG
>>>>> struct acpihp_dev_ops *hp_ops;
>>>>> #endif /* CONFIG_ACPI_HOTPLUG */
>>>>> };
>>>>>
>>>>> in hp_ops, we divide the prepare_remove into six small steps, that is:
>>>>> 1) pre_release(): optional step to mark device going to be removed/busy
>>>>> 2) release(): reclaim device from running system
>>>>> 3) post_release(): rollback if cancelled by user or error happened
>>>>> 4) pre_unconfigure(): optional step to solve possible dependency issue
>>>>> 5) unconfigure(): remove devices from running system
>>>>> 6) post_unconfigure(): free resources used by devices
>>>>>
>>>>> In this way, we can easily rollback if error happens.
>>>>> How do you think of this solution, any suggestion ? I think we can achieve
>>>>> a better way for sharing ideas. :)
>>>>
>>>> Yes, sharing idea is good. :) I do not know if we need all 6 steps (I
>>>> have not looked at all your changes yet..), but in my mind, a hot-plug
>>>> operation should be composed with the following 3 phases.
>>>>
>>>> 1. Validate phase - Verify if the request is a supported operation. All
>>>> known restrictions are verified at this phase. For instance, if a
>>>> hot-remove request involves kernel memory, it is failed in this phase.
>>>> Since this phase makes no change, no rollback is necessary to fail.
>>>
>>> Actually, we can't do it this way, because the conditions may change between
>>> the check and the execution. So the first phase needs to involve execution
>>> to some extent, although only as far as it remains reversible.
>>
>> For memory hot-remove, we can check if the target memory ranges are
>> within ZONE_MOVABLE. We should not allow user to change this setup
>> during hot-remove operation. Other things may be to check if a target
>> node contains cpu0 (until it is supported), the console UART (assuming
>> we cannot delete it), etc. We should avoid doing rollback as much as we
>> can.
>
> Yes, we can make some checks upfront as an optimization and fail early if
> the conditions are not met, but for correctness we need to repeat those
> checks later anyway. Once we've decided to go for the eject, the conditions
> must hold whatever happens.
Hi Rafael,
Another reason for us to split hotplug operations into minor/tiny
steps is to support cancellation other than error handling. Theoretical
it may take infinite time to hot-remove a memory device, so we should provide
an interface for user to cancel ongoing hot-removal operations. Currently that's
done by timeout in the memory hot-remove code path, but I think it not the
best solutions. We should provide choices to users:
1) wait for ever to remove a hot-removal operation
2) cancel an ongoing hot-removal operation if it takes too long
Regards!
Gerry
>
> Thanks,
> Rafael
>
>
next prev parent reply other threads:[~2012-12-06 17:07 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-23 17:50 [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation Vasilis Liaskovitis
2012-11-23 17:50 ` [RFC PATCH v3 1/3] acpi: Introduce prepare_remove operation in acpi_device_ops Vasilis Liaskovitis
2012-11-27 0:10 ` Toshi Kani
2012-11-27 18:36 ` Vasilis Liaskovitis
2012-11-27 23:18 ` Rafael J. Wysocki
2012-11-23 17:50 ` [RFC PATCH v3 2/3] acpi_memhotplug: Add prepare_remove operation Vasilis Liaskovitis
2012-11-24 16:23 ` Wen Congyang
2012-11-23 17:50 ` [RFC PATCH v3 3/3] acpi_memhotplug: Allow eject to proceed on rebind scenario Vasilis Liaskovitis
2012-11-24 16:20 ` Wen Congyang
2012-11-26 8:36 ` Vasilis Liaskovitis
2012-11-26 9:11 ` Wen Congyang
2012-11-27 0:19 ` Toshi Kani
2012-11-27 18:32 ` Vasilis Liaskovitis
2012-11-27 22:03 ` Toshi Kani
2012-11-27 23:41 ` Rafael J. Wysocki
2012-11-28 16:01 ` Toshi Kani
2012-11-28 18:40 ` Rafael J. Wysocki
2012-11-28 21:02 ` Toshi Kani
2012-11-28 21:40 ` Rafael J. Wysocki
2012-11-28 21:40 ` Toshi Kani
2012-11-28 22:01 ` Rafael J. Wysocki
2012-11-28 22:04 ` Toshi Kani
2012-11-28 22:21 ` Rafael J. Wysocki
2012-11-28 22:16 ` Toshi Kani
2012-11-28 22:39 ` Rafael J. Wysocki
2012-11-28 22:46 ` Greg KH
2012-11-28 23:05 ` Rafael J. Wysocki
2012-11-28 23:10 ` Greg KH
2012-11-28 23:31 ` Rafael J. Wysocki
2012-11-28 23:49 ` Rafael J. Wysocki
2012-11-29 1:02 ` Toshi Kani
2012-11-29 1:15 ` Toshi Kani
2012-11-29 10:03 ` Rafael J. Wysocki
2012-11-29 11:30 ` Vasilis Liaskovitis
2012-11-29 16:57 ` Rafael J. Wysocki
2012-11-29 17:56 ` Toshi Kani
2012-11-29 20:25 ` Rafael J. Wysocki
2012-11-29 20:38 ` Toshi Kani
2012-11-29 21:23 ` Rafael J. Wysocki
2012-11-29 21:46 ` Toshi Kani
2012-11-29 22:11 ` Rafael J. Wysocki
2012-11-29 23:17 ` Toshi Kani
2012-11-30 0:13 ` Rafael J. Wysocki
2012-11-30 1:09 ` Toshi Kani
2012-11-29 16:43 ` Toshi Kani
2012-11-29 11:04 ` Vasilis Liaskovitis
2012-11-29 17:44 ` Toshi Kani
2012-12-06 9:30 ` Vasilis Liaskovitis
2012-12-06 12:50 ` Rafael J. Wysocki
2012-12-06 15:41 ` Toshi Kani
2012-12-06 20:32 ` Rafael J. Wysocki
2012-11-28 11:05 ` [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation Hanjun Guo
2012-11-28 18:41 ` Toshi Kani
2012-11-29 4:48 ` Hanjun Guo
2012-11-29 22:27 ` Toshi Kani
2012-12-03 4:25 ` Hanjun Guo
2012-12-04 0:10 ` Toshi Kani
2012-12-04 9:16 ` Hanjun Guo
2012-12-04 23:23 ` Toshi Kani
2012-12-05 12:10 ` Hanjun Guo
2012-12-05 22:31 ` Toshi Kani
2012-12-06 16:47 ` Jiang Liu
2012-12-07 2:25 ` Toshi Kani
2012-12-06 16:40 ` Jiang Liu
2012-12-06 20:30 ` Rafael J. Wysocki
2012-12-07 2:57 ` Toshi Kani
2012-12-07 5:57 ` Jiang Liu
2012-12-08 1:08 ` Toshi Kani
2012-12-11 14:34 ` Jiang Liu
2012-12-13 14:42 ` Toshi Kani
2012-12-13 15:15 ` Jiang Liu
2012-12-15 1:19 ` Toshi Kani
2012-11-29 10:15 ` Rafael J. Wysocki
2012-11-29 11:36 ` Vasilis Liaskovitis
2012-12-06 16:59 ` Jiang Liu
2012-11-29 17:03 ` Toshi Kani
2012-11-29 20:30 ` Rafael J. Wysocki
2012-11-29 20:39 ` Toshi Kani
2012-11-29 20:56 ` Toshi Kani
2012-11-29 21:25 ` Rafael J. Wysocki
2012-12-06 17:10 ` Jiang Liu
2012-12-06 17:07 ` Jiang Liu [this message]
2012-12-06 17:01 ` Jiang Liu
2012-12-06 16:56 ` Jiang Liu
2012-12-06 16:00 ` Jiang Liu
2012-12-06 16:03 ` Toshi Kani
2012-12-06 16:25 ` Jiang Liu
2012-12-06 16:31 ` Toshi Kani
2012-12-06 16:52 ` Jiang Liu
2012-12-06 17:09 ` Toshi Kani
2012-12-06 17:30 ` Jiang Liu
2012-12-06 17:28 ` Toshi Kani
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