linux-kernel - Re: [PATCH v8] hugetlbfs: move lock assertions after early returns in huge_pmd

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Message-ID: <080b64d6-7bc3-4ba6-ab76-e1fe728bff88@sirena.org.uk>
Date: Wed, 22 Oct 2025 15:34:10 +0100
From: Mark Brown <broonie@...nel.org>
To: Deepanshu Kartikey <kartikey406@...il.com>
Cc: muchun.song@...ux.dev, osalvador@...e.de, david@...hat.com,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	syzbot+f26d7c75c26ec19790e7@...kaller.appspotmail.com
Subject: Re: [PATCH v8] hugetlbfs: move lock assertions after early returns
 in huge_pmd_unshare()

On Tue, Oct 14, 2025 at 05:03:44PM +0530, Deepanshu Kartikey wrote:
> When hugetlb_vmdelete_list() processes VMAs during truncate operations,
> it may encounter VMAs where huge_pmd_unshare() is called without the
> required shareable lock. This triggers an assertion failure in
> hugetlb_vma_assert_locked().

On current mainline this translates the test from a fail to a skip on
the Raspberry Pi 4:

# # -------------------------
# # running ./hugetlb-madvise
# # -------------------------
# # [SKIP]
# ok 6 hugetlb-madvise # SKIP
# # hugepages not supported

due to:

[    0.000000] Kernel command line: console=ttyS1,115200n8 root=/dev/nfs rw nfsroot=172.16.0.2:/var/lib/lava/dispatcher/tmp/1991635/extract-nfsrootfs-9ik0m73w,tcp,hard secretmem.enable hugepagesz=32M hugepages=0:4 default_hugepagesz=2M hugepages=0:128 hugepagesz=64K hugepages=0:4 kpti=off ip=dhcp
[    0.000000] Unknown kernel command line parameters "hugepagesz=64K hugepages=0:4 default_hugepagesz=2M", will be passed to user space.

which used to DTRT but I doubt is due to this specific patch...

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