linux-kernel - Re: [PATCH V2] PCI: AER: fix deadlock in do

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Message-ID: <alpine.LNX.2.20.1710021714260.30867@cae-iprp-alln-lb.cisco.com>
Date:   Mon, 2 Oct 2017 17:19:31 -0700
From:   Govindarajulu Varadarajan <gvaradar@...co.com>
To:     Sinan Kaya <okaya@...eaurora.org>
CC:     <benve@...co.com>, <bhelgaas@...gle.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <jlbec@...lplan.org>, <hch@....de>, <mingo@...hat.com>,
        <peterz@...radead.org>
Subject: Re: [PATCH V2] PCI: AER: fix deadlock in do_recovery

On Sat, 30 Sep 2017, Sinan Kaya wrote:

> On 9/30/2017 1:49 AM, Govindarajulu Varadarajan wrote:
>> This patch does a pci_bus_walk and adds all the devices to a list. After
>> unlocking (up_read) &pci_bus_sem, we go through the list and call
>> err_handler of the devices with devic_lock() held. This way, we dont try
>> to hold both locks at same time.
>
> I do like this approach with some more feedback.
>
> I need a little bit of help here from someone that knows get/put device calls.
>
> I understand get_device() and put_device() are there to increment/decrement
> reference counters. This patch seems to use them as an alternative for device_lock()
> and device_unlock() API.
>

get/put_deivce is not used as an alternative to device_lock() here. We are
incrementing the counter to make sure no one else free the device while they
are in our list. report_error_detected() and other cb will still acquire
device_lock().


> If this is a good assumption, then you can get away with just replacing device_lock()
> with get_device() and device_unlock() with put_device() in the existing code as
> well. Then, you don't need to build a linklist.