linux-kernel - Re: [RFC PATCH v1 06/22] PCI: use a global lock to serialize PCI root bridge hotplug operations

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Date:	Mon, 17 Sep 2012 23:51:22 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Don Dutile <ddutile@...hat.com>, Yinghai Lu <yinghai@...nel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	"Rafael J . Wysocki" <rjw@...k.pl>,
	Yijing Wang <wangyijing@...wei.com>,
	Xinwei Hu <huxinwei@...wei.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [RFC PATCH v1 06/22] PCI: use a global lock to serialize PCI
 root bridge hotplug operations

>>> I'm not sure why you didn't add a pci_host_bridge_hotplug_lock() in
>>> the sba_init() path, since it looks similar to the drm_open_helper()
>>> path above.  But in any case, I think that would be the wrong thing to
>>> do because it would fix the superficial problem while leaving the
>>> deeper problem of host bridge hot-add not setting the iommu pointer.
> 
>> sba_init is called during system initialization stages through subsys_initcall,
>> so no extra protection for it.
> 
> OK, I see your reasoning.  But I don't agree :)  All the users of an
> interface should use the same locking scheme, even if they're at
> boot-time where we "know" we don't need it.  It's too hard to analyze
> differences, and code gets copied from one place to somewhere else
> where it might not be appropriate.
Hi Bjorn,
	"All the users of an interface should use the same locking scheme", a really
good design pattern to follow. It's so easy for everybody to remove the __init
modifier without noticing the design limitation.
	--Gerry
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