Re: [bug report][PPC]: rmod nvme driver causes the kernel panic

[Nam Cao <namcao@linutronix.de>]

Nilay Shroff <nilay@linux.ibm.com> writes:
> Hi Nam,
Hi Nilay,

> On the latest upstream mainline kernel, I am encountering a kernel
> crash when attempting to unload the NVMe driver module (rmmod nvme)
> on a POWER9 system. The crash appears to be triggered by the recent
> work on using MSI parent domains, discussed here: 
> https://lore.kernel.org/all/cover.1754903590.git.namcao@linutronix.de/

Thanks for the detailed analysis. This should be fixed by:
https://lore.kernel.org/linuxppc-dev/20251010120307.3281720-1-namcao@linutronix.de/T/#u

which currently is in powerpc/fixes-test

> Possible Cause:
> ===============
> This looks like a cleanup ordering issue introduced by the recent MSI parent
> domain rework. The PCI/MSI teardown seems to assume that the MSI descriptor
> remains valid until after the domain teardown path executes — which no longer
> appears to hold true in this sequence.

I think the reason is more idiotic than that, the msi_alloc_info_t
passed to pseries_msi_ops_teardown() is always all zeroes, thus we have
the NULL pointer deref regardless of the sequence. See the patch I
mentioned.

Nam