From: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
To: akpm@linux-foundation.org, hannes@cmpxchg.org
Cc: david@kernel.org, mhocko@kernel.org, qi.zheng@linux.dev,
shakeel.butt@linux.dev, ljs@kernel.org, kasong@tencent.com,
baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com,
weixugc@google.com, baoquan.he@linux.dev,
baolin.wang@linux.alibaba.com, yuzhao@google.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
apais@microsoft.com, rlmenge@gmail.com,
Siddharth Chintamaneni <sidchintamaneni@gmail.com>,
stable@vger.kernel.org, Hardik Garg <hargar@linux.microsoft.com>
Subject: [PATCH v1] mm: multi-gen LRU: fix NULL lruvec->pgdat deref with memcg disabled on cmdline
Date: Sat, 17 Oct 2026 00:04:51 +0000 [thread overview]
Message-ID: <20261017000451.89536-1-sidchintamaneni@gmail.com> (raw)
When CONFIG_MEMCG=y, lruvec_pgdat() returns lruvec->pgdat, which for the
per-node pgdat->__lruvec is left NULL by lruvec_init() and only filled in
lazily by mem_cgroup_lruvec(). Normally that happens early, e.g. on the
first folio_add_lru().
With cgroup_disable=memory, lru_gen_shrink_node() passes &pgdat->__lruvec
directly to shrink_one(). If direct reclaim runs before anything has
called mem_cgroup_lruvec() for the node, which can happen during early
boot under memory pressure (e.g. a kdump kernel), get_swappiness() ends
up dereferencing a NULL pgdat:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000005040
pc : get_swappiness+0x68/0xb0
lr : try_to_shrink_lruvec+0x54/0x2c0
Call trace:
get_swappiness+0x68/0xb0 (P)
try_to_shrink_lruvec+0x54/0x2c0
shrink_one+0x8c/0x240
shrink_node+0xc6c/0xe08
do_try_to_free_pages+0xdc/0x570
try_to_free_pages+0x124/0x278
__alloc_frozen_pages_noprof+0x6e8/0xf78
alloc_pages_mpol+0xc4/0x1c0
alloc_frozen_pages_noprof+0x54/0xe8
alloc_pages_noprof+0x1c/0x40
atomic_pool_expand+0x98/0x300
__dma_atomic_pool_init+0x58/0xd8
dma_atomic_pool_init+0x154/0x170
do_one_initcall+0x64/0x350
kernel_init_freeable+0x214/0x430
kernel_init+0x2c/0x208
ret_from_fork+0x10/0x20
The classic LRU path and MGLRU before per-node lru_gen_folio lists
obtained the lruvec through mem_cgroup_lruvec(), which sets
lruvec->pgdat.
The above was hit on an arm64 kdump kernel (6.18-based) booted with
cgroup_disable=memory nr_cpus=4. It also reproduces on mainline on an
arm64 VM with CONFIG_ARM64_64K_PAGES=y, CONFIG_MEMCG=y,
CONFIG_LRU_GEN_ENABLED=y and:
mem=160M nr_cpus=4 coherent_pool=512M cgroup_disable=memory
These options only serve to force direct reclaim early in boot; with
160M the boot eventually ends in OOM regardless. On mainline the first
LRU reclaim happens while unpacking the initramfs, and faults the same
way:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000005040
pc : get_swappiness+0xd4/0x150
Call trace:
get_swappiness+0xd4/0x150 (P)
try_to_shrink_lruvec+0x44/0x2b8
shrink_one+0x80/0x1a0
shrink_node+0xd98/0xea8
do_try_to_free_pages+0xf4/0x4b0
try_to_free_pages+0x110/0x360
__alloc_frozen_pages_noprof+0x8b0/0x1718
...
__filemap_get_folio_mpol+0x2ac/0x548
simple_write_begin+0x44/0xf8
page_symlink+0x178/0x198
...
do_populate_rootfs+0x13c/0x200
Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Cc: stable@vger.kernel.org # 6.3+
Assisted-by: LLM
Signed-off-by: Siddharth Chintamaneni <sidchintamaneni@gmail.com>
Signed-off-by: Hardik Garg <hargar@linux.microsoft.com>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f11491ee9ed5..0c57e4f1eb15 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5253,7 +5253,7 @@ static void lru_gen_shrink_node(struct pglist_data *pgdat, struct scan_control *
sc->nr_reclaimed = 0;
if (mem_cgroup_disabled())
- shrink_one(&pgdat->__lruvec, sc);
+ shrink_one(mem_cgroup_lruvec(NULL, pgdat), sc);
else
shrink_many(pgdat, sc);
--
2.45.4
reply other threads:[~2026-10-17 0:04 UTC|newest]
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