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

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Date: Fri, 28 Jun 2024 15:34:37 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Bjorn Helgaas <helgaas@...nel.org>, Krishna Kumar <krishnak@...ux.ibm.com>
Cc: 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

Bjorn Helgaas <helgaas@...nel.org> writes:
> I expect this series would go through the powerpc tree since that's
> where most of the chance is.

Thanks, yeah I'll plan to merge v4 with your comments addressed.

cheers

> 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
>>