Re: [PATCH v2] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest

[Amit Machhiwal]

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@xxxxxxx> 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.

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