linux-kernel - Re: [PATCH v3 1/2] pci/hotplug/pnv_php: Fix hotplug driver crash on Powernv

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Date: Wed, 26 Jun 2024 10:21:54 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Krishna Kumar <krishnak@...ux.ibm.com>
Cc: mpe@...erman.id.au, npiggin@...il.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	brking@...ux.vnet.ibm.com, gbatra@...ux.ibm.com,
	aneesh.kumar@...nel.org, christophe.leroy@...roup.eu,
	nathanl@...ux.ibm.com, bhelgaas@...gle.com, oohall@...il.com,
	tpearson@...torengineering.com, mahesh.salgaonkar@...ibm.com
Subject: Re: [PATCH v3 1/2] pci/hotplug/pnv_php: Fix hotplug driver crash on
 Powernv

I expect this series would go through the powerpc tree since that's
where most of the chance is.

On Mon, Jun 24, 2024 at 05:39:27PM +0530, 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 unregistartion the code was
> again trying to explicitly disable the msi which causes the Null pointer
> dereference and kernel crash.

s/unregistartion/unregistration/
s/Null/NULL/ to match previous use
s/msi/MSI/ to match spec usage

> Proposed Fix : The fix is to correct the check during unregistration path
> so that the code should not  try to invoke pci_disable_msi/msix() if its
> data structure is already freed.

s/Proposed Fix : The fix is to// ... Just say what the patch does.

If/when the powerpc folks like this, add my:

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Gaurav Batra <gbatra@...ux.ibm.com>
> Cc: Nathan Lynch <nathanl@...ux.ibm.com>
> Cc: Brian King <brking@...ux.vnet.ibm.com>
> 
> Signed-off-by: Krishna Kumar <krishnak@...ux.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)
> -- 
> 2.45.0
>