linux-kernel - Regression: NULL pointer dereference after NFS_V4_2_READ

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Date:   Sat, 7 Jan 2023 16:44:55 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Anna Schumaker <Anna.Schumaker@...app.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>
Cc:     linux-nfs@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Subject: Regression: NULL pointer dereference after NFS_V4_2_READ_PLUS (commit
 7fd461c47)

Hi,

Bisect identified commit 7fd461c47c6c ("NFSv4.2: Change the default
KConfig value for READ_PLUS") as one leading to NULL pointer exception
when mounting NFS root on NFSv4 client:

[   25.739003] systemd[1]: Set hostname to <odroidhc1>.
[   25.771714] systemd[1]: Failed to bump fs.file-max, ignoring: Invalid
argument
[   26.199478] 8<--- cut here ---
[   26.201366] Unable to handle kernel NULL pointer dereference at
virtual address 00000004
...
[   26.555522]  mmiocpy from xdr_inline_decode+0xec/0x16c
[   26.560628]  xdr_inline_decode from nfs4_xdr_dec_read_plus+0x178/0x358
[   26.567130]  nfs4_xdr_dec_read_plus from call_decode+0x204/0x304

Full OOPS attached. Full log available here:
https://krzk.eu/#/builders/21/builds/3901/steps/15/logs/serial0

Disabling NFS_V4_2_READ_PLUS fixes the issue, so obviously the commit is
not the cause, but rather making it default caused the regression.

I did not make the bisect yet which commit introduced it, if every
config includes NFS_V4_2_READ_PLUS.

Some details about platform:

1. Arch ARM Linux
2. exynos_defconfig
3. Odroid HC1 board with ARMv7, octa-core (Cortex-A7+A15), Exynos5422 SoC
4. systemd, boot up with static IP set in kernel command line
5. No swap
6. Kernel, DTB and initramfs are downloaded with TFTP
7. NFS root (NFS client) mounted from a NFSv4 server

Best regards,
Krzysztof
View attachment "log.txt" of type "text/plain" (5913 bytes)