linux-kernel - Re: [PATCH v4 07/18] nitro_enclaves: Init misc device providing the ioctl interface

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Message-ID: <7166a6aa-2e8f-fed9-6b95-f53b823e5bb7@amazon.com>
Date:   Tue, 30 Jun 2020 12:08:18 +0300
From:   "Paraschiv, Andra-Irina" <andraprs@...zon.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>,
        Anthony Liguori <aliguori@...zon.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Colm MacCarthaigh <colmmacc@...zon.com>,
        Bjoern Doebel <doebel@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Frank van der Linden <fllinden@...zon.com>,
        "Alexander Graf" <graf@...zon.de>,
        Martin Pohlack <mpohlack@...zon.de>,
        Matt Wilson <msw@...zon.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Balbir Singh <sblbir@...zon.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "Stefan Hajnoczi" <stefanha@...hat.com>,
        Stewart Smith <trawets@...zon.com>,
        "Uwe Dannowski" <uwed@...zon.de>, <kvm@...r.kernel.org>,
        <ne-devel-upstream@...zon.com>
Subject: Re: [PATCH v4 07/18] nitro_enclaves: Init misc device providing the
 ioctl interface



On 30/06/2020 11:05, Greg KH wrote:
>
> On Mon, Jun 29, 2020 at 08:45:25PM +0300, Paraschiv, Andra-Irina wrote:
>>
>> On 29/06/2020 19:20, Greg KH wrote:
>>> On Mon, Jun 22, 2020 at 11:03:18PM +0300, Andra Paraschiv wrote:
>>>> +static int __init ne_init(void)
>>>> +{
>>>> +     struct pci_dev *pdev = pci_get_device(PCI_VENDOR_ID_AMAZON,
>>>> +                                           PCI_DEVICE_ID_NE, NULL);
>>>> +     int rc = -EINVAL;
>>>> +
>>>> +     if (!pdev)
>>>> +             return -ENODEV;
>>> Ick, that's a _very_ old-school way of binding to a pci device.  Please
>>> just be a "real" pci driver and your probe function will be called if
>>> your hardware is present (or when it shows up.)  To do it this way
>>> prevents your driver from being auto-loaded for when your hardware is
>>> seen in the system, as well as lots of other things.
>> This check is mainly here in the case any codebase is added before the pci
>> driver register call below.
> What do you mean by "codebase"?  You control this driver, just do all of
> the logic in the probe() function, no need to do this in the module init
> call.
>
>> And if we log any error with dev_err() instead of pr_err() before the driver
>> register.
> Don't do that.
>
>> That check was only for logging purposes, if done with dev_err(). I removed
>> the check in v5.
> Again, don't do it :)
>
>>>> +
>>>> +     if (!zalloc_cpumask_var(&ne_cpu_pool.avail, GFP_KERNEL))
>>>> +             return -ENOMEM;
>>>> +
>>>> +     mutex_init(&ne_cpu_pool.mutex);
>>>> +
>>>> +     rc = pci_register_driver(&ne_pci_driver);
>>> Nice, you did it right here, but why the above crazy test?
>>>
>>>> +     if (rc < 0) {
>>>> +             dev_err(&pdev->dev,
>>>> +                     "Error in pci register driver [rc=%d]\n", rc);
>>>> +
>>>> +             goto free_cpumask;
>>>> +     }
>>>> +
>>>> +     return 0;
>>> You leaked a reference on that pci device, didn't you?  Not good :(
>> Yes, the pci get device call needs its pair - pci_dev_put(). I added it here
>> and for the other occurrences where it was missing.
> Again, just don't do it and then you don't have to worry about any of
> this.

Yup, already started this morning to check & update where we can go 
without this call to get a PCI device reference, as a follow-up to what 
we discussed yesterday.

Thanks,
Andra



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