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

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Message-ID: <87h5w3f7ed.fsf@yellow.woof>
Date: Mon, 13 Oct 2025 12:00:42 +0200
From: Nam Cao <namcao@...utronix.de>
To: Nilay Shroff <nilay@...ux.ibm.com>
Cc: maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
 christophe.leroy@...roup.eu, tglx@...utronix.de, maz@...nel.org,
 gautam@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org, Linux List Kernel
 Mailing <linux-kernel@...r.kernel.org>, "linux-nvme@...ts.infradead.org"
 <linux-nvme@...ts.infradead.org>
Subject: Re: [bug report][PPC]: rmod nvme driver causes the kernel panic

Nilay Shroff <nilay@...ux.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