linux-kernel - Re: [PATCH v2] PCI: Fix crash during pci

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Message-ID: <af45d85c-2145-cbce-b91b-2aa70a9dcd0f@amd.com>
Date: Mon, 29 Jul 2024 09:47:37 -0700
From: Lizhi Hou <lizhi.hou@....com>
To: Rob Herring <robh@...nel.org>, <devicetree@...r.kernel.org>, Saravana
 Kannan <saravanak@...gle.com>, Kowshik Jois B S <kowsjois@...ux.ibm.com>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kvm-ppc@...r.kernel.org>, Vaidyanathan Srinivasan <svaidy@...ux.ibm.com>,
	Lukas Wunner <lukas@...ner.de>, Nicholas Piggin <npiggin@...il.com>, Bjorn
 Helgaas <bhelgaas@...gle.com>, Vaibhav Jain <vaibhav@...ux.ibm.com>,
	<linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2] PCI: Fix crash during pci_dev hot-unplug on pseries
 KVM guest

Hi Amit

On 7/29/24 04:13, Amit Machhiwal wrote:
> Hi Lizhi,
>
> On 2024/07/26 11:45 AM, Lizhi Hou wrote:
>> On 7/26/24 10:52, Rob Herring wrote:
>>> On Thu, Jul 25, 2024 at 6:06 PM Lizhi Hou <lizhi.hou@....com> wrote:
>>>> Hi Amit,
>>>>
>>>>
>>>> I try to follow the option which add a OF flag. If Rob is ok with this,
>>>> I would suggest to use it instead of V1 patch
>>>>
>>>> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
>>>> index dda6092e6d3a..a401ed0463d9 100644
>>>> --- a/drivers/of/dynamic.c
>>>> +++ b/drivers/of/dynamic.c
>>>> @@ -382,6 +382,11 @@ void of_node_release(struct kobject *kobj)
>>>>                                   __func__, node);
>>>>            }
>>>>
>>>> +       if (of_node_check_flag(node, OF_CREATED_WITH_CSET)) {
>>>> +               of_changeset_revert(node->data);
>>>> +               of_changeset_destroy(node->data);
>>>> +       }
>>> What happens if multiple nodes are created in the changeset?
>> Ok. multiple nodes will not work.
>>>> +
>>>>            if (node->child)
>>>>                    pr_err("ERROR: %s() unexpected children for %pOF/%s\n",
>>>>                            __func__, node->parent, node->full_name);
>>>> @@ -507,6 +512,7 @@ struct device_node *of_changeset_create_node(struct
>>>> of_changeset *ocs,
>>>>            np = __of_node_dup(NULL, full_name);
>>>>            if (!np)
>>>>                    return NULL;
>>>> +       of_node_set_flag(np, OF_CREATED_WITH_CSET);
>>> This should be set where the data ptr is set.
>> Ok. It sounds the fix could be simplified to 3 lines change.
> Thanks for the patch. The hot-plug and hot-unplug of PCI device seem to work
> fine as expected. I see this patch would attempt to remove only the nodes which
> were created in `of_pci_make_dev_node()` with the help of the newly introduced
> flag, which looks good to me.
>
> Also, since a call to `of_pci_make_dev_node()` from `pci_bus_add_device()`, that
> creates devices nodes only for bridge devices, is conditional on
> `pci_is_bridge()`, it only makes sense to retain the logical symmetry and call
> `of_pci_remove_node()` conditionally on `pci_is_bridge()` as well in
> `pci_stop_dev()`. Hence, I would like to propose the below change along with the
> above patch:
>
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index 910387e5bdbf..c6394bf562cd 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -23,7 +23,8 @@ static void pci_stop_dev(struct pci_dev *dev)
>                  device_release_driver(&dev->dev);
>                  pci_proc_detach_device(dev);
>                  pci_remove_sysfs_dev_files(dev);
> -               of_pci_remove_node(dev);
> +               if (pci_is_bridge(dev))
> +                       of_pci_remove_node(dev);
>   
>                  pci_dev_assign_added(dev, false);
>          }
>
> Please let me know of your thoughts on this and based on that I can spin the v3
> of this patch.

As I mentioned, there are endpoints in pci quirks (pci/quirks.c) will 
also create nodes by of_pci_make_dev_node(). So please remove above two 
lines.


Thanks,

Lizhi

>
> In addition to this, can this patch be taken as part of 6.11 as a bug fix?
>
> Thanks,
> Amit
>
>>
>> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
>> index 51e3dd0ea5ab..0b3ba1e1b18c 100644
>> --- a/drivers/pci/of.c
>> +++ b/drivers/pci/of.c
>> @@ -613,7 +613,7 @@ void of_pci_remove_node(struct pci_dev *pdev)
>>          struct device_node *np;
>>
>>          np = pci_device_to_OF_node(pdev);
>> -       if (!np || !of_node_check_flag(np, OF_DYNAMIC))
>> +       if (!np || !of_node_check_flag(np, OF_CREATED_WITH_CSET))
>>                  return;
>>          pdev->dev.of_node = NULL;
>>
>> @@ -672,6 +672,7 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
>>          if (ret)
>>                  goto out_free_node;
>>
>> +       of_node_set_flag(np, OF_CREATED_WITH_CSET);
>>          np->data = cset;
>>          pdev->dev.of_node = np;
>>          kfree(name);
>> diff --git a/include/linux/of.h b/include/linux/of.h
>> index a0bedd038a05..a46317f6626e 100644
>> --- a/include/linux/of.h
>> +++ b/include/linux/of.h
>> @@ -153,6 +153,7 @@ extern struct device_node *of_stdout;
>>   #define OF_POPULATED_BUS       4 /* platform bus created for children */
>>   #define OF_OVERLAY             5 /* allocated for an overlay */
>>   #define OF_OVERLAY_FREE_CSET   6 /* in overlay cset being freed */
>> +#define OF_CREATED_WITH_CSET    7 /* created by of_changeset_create_node */
>>
>>   #define OF_BAD_ADDR    ((u64)-1)
>>
>>
>> Lizhi
>>
>>> Rob