Re: [PATCHv2 4/4] PCI/AER: Covertly inject errors with ftrace hooks

[Keith Busch <keith.busch@intel.com>]

On Thu, Oct 11, 2018 at 02:41:46PM -0500, Bjorn Helgaas wrote:
> On Thu, Oct 11, 2018 at 12:34:13PM -0600, Keith Busch wrote:
> > The aer_inject module had been intercepting config requests by overwriting
> > the config accessor operations in the pci_bus ops.  This has several
> > issues.
> > 
> > First, the module was tracking kernel objects unbeknownst to the drivers
> > that own them.  The kernel may free those devices, leaving the AER inject
> > module holding stale references and no way to know that happened.
> > 
> > Second, the PCI enumeration has child devices inherit pci_bus ops from
> > the parent bus.  Since errors may lead to link resets that trigger
> > re-enumeration, the child devices would inherit operations that don't
> > know about the devices using them, causing kernel crashes.
> > 
> > Finally, CONFIG_PCI_LOCKLESS_CONFIG doesn't block accessing the pci_bus
> > ops, so it's racing with potential in-flight config requests.
> > 
> > This patch uses a different error injection approach leveraging ftrace
> > to thunk the config space functions.  If the kernel and architecture
> > are capable, the ftrace hook will overwrite the processor's function
> > call address with the error injection function. This discreet error
> > injection doesn't modify or track driver structures, fixing the issues
> > with the current method.
> > 
> > If either the kernel config or platform arch do not support the necessary
> > ftrace capabilities, the aer_inject module will fallback to the older
> > way so that it may continue to be used as before.
> 
> I dropped this patch for now because the 0-day robot found something wrong.

I just saw that. Sorry for the trouble. It fails a minimal kernel
config, so I missed checking appropriate config defines.