linux-kernel - Re: [PATCH] mm/kmsan: Fix kmsan kmalloc hook when no stack depots are allocated yet

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Message-ID: <CAG_fn=UQYdGqiMbFxp+XTgP=zkZgDGgdcA74Zcs9HTo+zd3oYA@mail.gmail.com>
Date: Fri, 31 Oct 2025 12:57:01 +0100
From: Alexander Potapenko <glider@...gle.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, 
	Harry Yoo <harry.yoo@...cle.com>, Michal Hocko <mhocko@...e.com>, 
	Shakeel Butt <shakeel.butt@...ux.dev>, Eric Biggers <ebiggers@...nel.org>, 
	Aleksei Nikiforov <aleksei.nikiforov@...ux.ibm.com>, Marco Elver <elver@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev <kasan-dev@...glegroups.com>, 
	linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, 
	Ilya Leoshkevich <iii@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH] mm/kmsan: Fix kmsan kmalloc hook when no stack depots are
 allocated yet

> What's puzzling is that it took 9 month to discover it ?!
> and allegedly Eric is seeing it by running kmsan selftest,
> but Alexander couldn't repro it initially?

If I understand correctly, Eric was linking his tests into the kernel
(CONFIG_KMSAN_KUNIT_TEST=y was implicitly set because
CONFIG_MODULES=n), whereas I ran them as a module.
After the kernel booted up, the stack depot was already initialized,
so the tests behaved just fine.
KMSAN also continued to work normally on syzbot and report bugs (see
https://syzkaller.appspot.com/upstream/graph/found-bugs), so it wasn't
really obvious that something was broken.

> Looks like there is a gap in kmsan test coverage.
> People that care about kmsan should really step up.

You are right, we should add KMSAN KUnit tests to some CI (wonder if
there are KernelCI instances allowing that?)
I'll look into that.