[PATCH v4 1/2] pci/hotplug/pnv_php: Fix hotplug driver crash on Powernv

[Krishna Kumar]

Hi Michael,

When you apply/merge the patch, please consider below URL in commit message.
This is the URL where this issue was reported - 

https://lists.ozlabs.org/pipermail/linuxppc-dev/2023-December/267034.html

Thanks, 
Krishna


On 7/1/24 1:15 PM, Krishna Kumar wrote:
> Description of the problem: The hotplug driver for powerpc
> (pci/hotplug/pnv_php.c) gives kernel crash when we try to
> hot-unplug/disable the PCIe switch/bridge from the PHB.
>
> Root Cause of Crash: The crash is due to the reason that, though the msi
> data structure has been released during disable/hot-unplug path and it
> has been assigned with NULL, still during unregistration the code was
> again trying to explicitly disable the MSI which causes the NULL pointer
> dereference and kernel crash.
>
> The patch fixes the check during unregistration path to prevent invoking
> pci_disable_msi/msix() since its data structure is already freed.
>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Nicholas Piggin <npiggin at gmail.com>
> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar at kernel.org>
> Cc: Bjorn Helgaas <bhelgaas at google.com>
> Cc: Gaurav Batra <gbatra at linux.ibm.com>
> Cc: Nathan Lynch <nathanl at linux.ibm.com>
> Cc: Brian King <brking at linux.vnet.ibm.com>
>
> Acked-by: Bjorn Helgaas <bhelgaas at google.com>
> Tested-by: Shawn Anastasio <sanastasio at raptorengineering.com>
> Signed-off-by: Krishna Kumar <krishnak at linux.ibm.com>
> ---
>  drivers/pci/hotplug/pnv_php.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pnv_php.c b/drivers/pci/hotplug/pnv_php.c
> index 694349be9d0a..573a41869c15 100644
> --- a/drivers/pci/hotplug/pnv_php.c
> +++ b/drivers/pci/hotplug/pnv_php.c
> @@ -40,7 +40,6 @@ static void pnv_php_disable_irq(struct pnv_php_slot *php_slot,
>  				bool disable_device)
>  {
>  	struct pci_dev *pdev = php_slot->pdev;
> -	int irq = php_slot->irq;
>  	u16 ctrl;
>  
>  	if (php_slot->irq > 0) {
> @@ -59,7 +58,7 @@ static void pnv_php_disable_irq(struct pnv_php_slot *php_slot,
>  		php_slot->wq = NULL;
>  	}
>  
> -	if (disable_device || irq > 0) {
> +	if (disable_device) {
>  		if (pdev->msix_enabled)
>  			pci_disable_msix(pdev);
>  		else if (pdev->msi_enabled)