Re: [PATCH 1/2] devcoredump: Remove devcoredump device if failing device is gone

[Mukesh Ojha]

On 1/29/2024 11:18 PM, Johannes Berg wrote:
> On Fri, 2024-01-26 at 10:11 -0500, Rodrigo Vivi wrote:
> > Make dev_coredumpm a real device managed helper, that not only
> > frees the device after a scheduled delay (DEVCD_TIMEOUT), but
> > also when the failing/crashed device is gone.
> >
> > The module remove for the drivers using devcoredump are currently
> > broken if attempted between the crash and the DEVCD_TIMEOUT, since
> > the symbolic sysfs link won't be deleted.
>
> Hmm, is it a problem to remove a whole dev when it still has some link
> here? Maybe we could just make the link be managed/auto-removed?
>
> Probably regardless of that you should change the comment in
> devcd_dev_release() since it's no longer a concern?
>
> > On top of that, for PCI devices, the unbind of the device will
> > call the pci .remove void function, that cannot fail. At that
> > time, our device is pretty much gone, but the read and free
> > functions are alive trough the devcoredump device and they
>                        ^ through, I guess
>
> > can get some NULL dereferences or use after free.
>
> Not sure I understand this part, how's this related to PCI's .remove?
>
> > So, if the failing-device is gone let's also request for the
> > devcoredump-device removal using the same mod_delayed_work
> > as when writing anything through data. The flush cannot be
> > used since it is synchronous and the devcd would be surely
> > gone right before the mutex_unlock on the next line.
>
> Can we just decouple it instead and remove the symlink? Which is kind of
> what the comment in devcd_dev_release() says but at the time I wasn't
> aware of all the devm mechanics etc.

Are we going to do this ?

-Mukesh

> I'm thinking this might be annoying in certain recovery cases, e.g.
> iwlwifi uses this but may sometimes unbind/rebind itself to recover from
> certain errors, and that'd make the FW dumps disappear.
>
> johannes