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

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Message-ID: <4826c905-720d-43bf-98a8-c4be076a3ebe@raptorengineering.com>
Date: Thu, 27 Jun 2024 12:04:03 -0500
From: Shawn Anastasio <sanastasio@...torengineering.com>
To: Krishna Kumar <krishnak@...ux.ibm.com>, mpe@...erman.id.au,
 npiggin@...il.com
Cc: nathanl@...ux.ibm.com, aneesh.kumar@...nel.org,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 gbatra@...ux.ibm.com, bhelgaas@...gle.com, tpearson@...torengineering.com,
 oohall@...il.com, brking@...ux.vnet.ibm.com, mahesh.salgaonkar@...ibm.com,
 linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/2] pci/hotplug/pnv_php: Fix hotplug driver crash on
 Powernv

Hi Krishna,

On 5/9/24 7:05 AM, 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.
> 
> 
> 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.
> 
> 
> Signed-off-by: Krishna Kumar <krishnak@...ux.ibm.com>

I've tested this on a POWER9 box and can confirm that it fixes the panics
when hotplugging PCIe bridges.

Tested-by: Shawn Anastasio <sanastasio@...torengineering.com>

Thanks,
Shawn