linux-kernel - Re: [PATCH v2 04/19] PCI: serialize hotplug operations triggered by PCI hotplug sysfs interfaces

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Message-id: <4FA0E02F.5040901@huawei.com>
Date:	Wed, 02 May 2012 15:20:15 +0800
From:	Jiang Liu <jiang.liu@...wei.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Jiang Liu <liuj97@...il.com>, Yinghai Lu <yinghai@...nel.org>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Don Dutile <ddutile@...hat.com>,
	Keping Chen <chenkeping@...wei.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 04/19] PCI: serialize hotplug operations triggered by
 PCI hotplug sysfs interfaces

On 2012-5-2 13:06, Greg KH wrote:
> On Fri, Apr 27, 2012 at 11:16:45PM +0800, Jiang Liu wrote:
>> +	/* Avoid deadlock with pci_hp_deregister() */
>> +	while (!pci_hotplug_try_enter()) {
>> +		/* Check whether the slot has been deregistered. */
>> +		if (list_empty(&slot->slot_list)) {
>> +			retval = -ENODEV;
>> +			goto exit_put;
>> +		}
>> +		msleep(1);
>> +	}
>
> Oh my.
>
> Wow.
>
> {sigh}
>
> ick.
>
> My eyes hurt.
>
> And your cpu load just went crazy.
>
> You can now handle all of the nasty emails from sysadmins asking why
> their systems look like their load is high for no good reason.
My bad, should use schedule_timeout_interruptible() instead of
msleep(1) here to avoid busy waiting.

>
> Not to mention all of the other issues here.
>
> My statement about not inventing new lock types has now been proven
> true.
>
> The fact that this would even be a chunk of code that was proposed to be
> merged makes me weep.
>
> You owe me a bottle of whatever you are drinking if you expect me to
> continue to review these patch submissions.
>
> I'm stopping here in the series, please rework this whole thing in a
> major way.
>
> greg k-h
>
>


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