linux-kernel - [REGRESSION, BISECTED] IPv6 RA is broken with Linux 6.12.42+

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Message-ID: <CALjTZvZkDr8N18ocZ8jNND_4DwKqr-PV4BBXB60+=WXPF3vn=Q@mail.gmail.com>
Date: Fri, 22 Aug 2025 17:35:22 +0100
From: Rui Salvaterra <rsalvaterra@...il.com>
To: wangzijie1@...or.com, gregkh@...uxfoundation.org
Cc: adobriyan@...il.com, viro@...iv.linux.org.uk, akpm@...ux-foundation.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	openwrt-devel@...ts.openwrt.org
Subject: [REGRESSION, BISECTED] IPv6 RA is broken with Linux 6.12.42+

Hi, everyone,


We noticed a regression in OpenWrt, with IPv6, which causes a router's
client devices to stop receiving the IPv6 default route. I have
bisected it down to (rather surprisingly)
fc1072d934f687e1221d685cf1a49a5068318f34 ("proc: use the same
treatment to check proc_lseek as ones for proc_read_iter et.al").
Reverting the aforementioned commit fixes the issue, of course.

Git bisect log follows:

git bisect start
# status: waiting for both good and bad commits
# bad: [880e4ff5d6c8dc6b660f163a0e9b68b898cc6310] Linux 6.12.42
git bisect bad 880e4ff5d6c8dc6b660f163a0e9b68b898cc6310
# status: waiting for good commit(s), bad commit known
# good: [8f5ff9784f3262e6e85c68d86f8b7931827f2983] Linux 6.12.41
git bisect good 8f5ff9784f3262e6e85c68d86f8b7931827f2983
# good: [dab173bae3303f074f063750a8dead2550d8c782] RDMA/hns: Fix
double destruction of rsv_qp
git bisect good dab173bae3303f074f063750a8dead2550d8c782
# bad: [11fa01706a4f60e759fbee7c53095ff22eaf1595] PCI: pnv_php: Work
around switches with broken presence detection
git bisect bad 11fa01706a4f60e759fbee7c53095ff22eaf1595
# bad: [966460bace9e1dd8609c9d44cf4509844daea8bb] perf record: Cache
build-ID of hit DSOs only
git bisect bad 966460bace9e1dd8609c9d44cf4509844daea8bb
# bad: [f63bd615e58f43dbe4b2e4c3f3ffa0bfb7766007] hwrng: mtk - handle
devm_pm_runtime_enable errors
git bisect bad f63bd615e58f43dbe4b2e4c3f3ffa0bfb7766007
# bad: [9ea3f6b9a67be3476e331ce51cac316c2614a564] pinmux: fix race
causing mux_owner NULL with active mux_usecount
git bisect bad 9ea3f6b9a67be3476e331ce51cac316c2614a564
# good: [1209e33fe3afb6d9e543f963d41b30cfc04538ff] RDMA/hns: Get
message length of ack_req from FW
git bisect good 1209e33fe3afb6d9e543f963d41b30cfc04538ff
# good: [5f3c0301540bc27e74abbfbe31571e017957251b] RDMA/hns: Fix
-Wframe-larger-than issue
git bisect good 5f3c0301540bc27e74abbfbe31571e017957251b
# bad: [fc1072d934f687e1221d685cf1a49a5068318f34] proc: use the same
treatment to check proc_lseek as ones for proc_read_iter et.al
git bisect bad fc1072d934f687e1221d685cf1a49a5068318f34
# good: [ec437d0159681bbdb1cf1f26759d12e9650bffca] kernel: trace:
preemptirq_delay_test: use offstack cpu mask
git bisect good ec437d0159681bbdb1cf1f26759d12e9650bffca
# first bad commit: [fc1072d934f687e1221d685cf1a49a5068318f34] proc:
use the same treatment to check proc_lseek as ones for proc_read_iter
et.al

Please let me know if you need any additional information.


Kind regards,

Rui Salvaterra