linux-kernel - Re: [PATCH] x86/PCI: Fully disable devices before releasing IRQ resource

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Date:	Fri, 13 Mar 2015 09:49:06 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	"Luck, Tony" <tony.luck@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"bp@...en8.de" <bp@...en8.de>, "Zheng, Lv" <lv.zheng@...el.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/PCI: Fully disable devices before releasing IRQ resource



On 2015/3/13 0:08, Rafael J. Wysocki wrote:
> On Thursday, March 12, 2015 09:41:21 AM Jiang Liu wrote:
>> On 2015/3/12 9:17, Rafael J. Wysocki wrote:
>>> On Wednesday, March 11, 2015 10:04:42 PM Luck, Tony wrote:
>>>>>> Unfortunately there's a long standing comment in pci_device_remove():
>>>>>>
>>>>>>         /*
>>>>>>          * We would love to complain here if pci_dev->is_enabled is set, that
>>>>>>          * the driver should have called pci_disable_device(), but the
>>>>>>          * unfortunate fact is there are too many odd BIOS and bridge setups
>>>>>>          * that don't like drivers doing that all of the time.
>>>>>>          * Oh well, we can dream of sane hardware when we sleep, no matter how
>>>>>>          * horrible the crap we have to deal with is when we are awake...
>>>>>>          */
>>>>>>
>>>>>> So, unless we can somehow ignore that comment, I suspect forcing the
>>>>>> device to be disabled on driver remove, whether done from pci-core or
>>>>>> from x86/pci, is going to cause all sorts of breakage.  Are the
>>>>>> expectations set by b4b55cda5874 really valid?  It seems like something
>>>>>> needs to be done to allow the IRQ to be automatically re-established on
>>>>>> x86 regardless of the driver doing the right thing when releasing the
>>>>>> device.  We're still looking at a regression for v4.0 as a result of
>>>>>> b4b55cda5874.
>>>>>
>>>>> In which case we probably should revert commit b4b55cda5874 for the time being.
>>>>>
>>>>> At least I'd be very nervous about any ad-hoc fixes at this stage of the cycle.
>>>>
>>>> The comment goes back to the dawn of "git" time ... not sure how much further
>>>> back.
>>>>
>>>> Is this actually still an issue on modern systems?  Maybe we need a black list
>>>> or white list to separate the good from bad systems?
>>>
>>> The answer to that is "We don't know" and in my not so humble opinion it is too
>>> risky to try to find out at the end of the cycle.
>> Hi Rafael and Alex,
>> How about a patch which:
>> 1) gives a warning if PCI device is still enabled when unloading driver
> 
> That may become sort of noisy.  I really would prefer to introduce things like
> that by the beginning of the cycle, not by the end of it.
Will try this on next merging window.

>> 2) release PCI interrupt only if PCI device is disabled.
>> By this way, we could support IOAPIC hot-removal on latest platforms and
>> avoid regressions on old platforms.
> 
> Well, please submit a patch for discussion.
> 
> I would like to know Bjorn's opinion about that too at least.
Still testing the patch, will send it out soon.

> 
> Rafael
> 
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