[moderation] [mm?] KCSAN: data-race in shmem_fallocate / shmem_writeout

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d3eeb99bbc99 Merge tag 'block-6.19-20260116' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=155f3522580000
kernel config: https://syzkaller.appspot.com/x/.config?x=676c6f0212d0c041
dashboard link: https://syzkaller.appspot.com/bug?extid=aae8bd56cc1c38d50ec4
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [ak...@linux-foundation.org baoli...@linux.alibaba.com hu...@google.com linux-...@vger.kernel.org linu...@kvack.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/68bc1a56de03/disk-d3eeb99b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cd8ba08f6c11/vmlinux-d3eeb99b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5277aa9db6a3/bzImage-d3eeb99b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aae8bd...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in shmem_fallocate / shmem_writeout

write to 0xffffc9000c3c3cb0 of 8 bytes by task 8171 on cpu 0:
shmem_fallocate+0x724/0x920 mm/shmem.c:3807
vfs_fallocate+0x3b6/0x400 fs/open.c:339
ioctl_preallocate fs/ioctl.c:289 [inline]
file_ioctl+0x4e3/0x5c0 fs/ioctl.c:-1
do_vfs_ioctl+0x7c9/0xe70 fs/ioctl.c:576
__do_sys_ioctl fs/ioctl.c:595 [inline]
__se_sys_ioctl+0x82/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffc9000c3c3cb0 of 8 bytes by task 8167 on cpu 1:
shmem_writeout+0x2c1/0x920 mm/shmem.c:1626
writeout mm/vmscan.c:649 [inline]
pageout mm/vmscan.c:698 [inline]
shrink_folio_list+0x1e75/0x2710 mm/vmscan.c:1418
evict_folios+0x2a4e/0x35b0 mm/vmscan.c:4711
try_to_shrink_lruvec+0x5f6/0x960 mm/vmscan.c:4874
lru_gen_shrink_lruvec mm/vmscan.c:5023 [inline]
shrink_lruvec+0x24e/0x1bc0 mm/vmscan.c:5784
shrink_node_memcgs mm/vmscan.c:6020 [inline]
shrink_node+0x68e/0x2000 mm/vmscan.c:6061
shrink_zones mm/vmscan.c:6300 [inline]
do_try_to_free_pages+0x404/0xcc0 mm/vmscan.c:6362
try_to_free_mem_cgroup_pages+0x222/0x470 mm/vmscan.c:6690
try_charge_memcg+0x37e/0xa10 mm/memcontrol.c:2388
obj_cgroup_charge_pages+0xa6/0x150 mm/memcontrol.c:2823
__memcg_kmem_charge_page+0x9e/0x170 mm/memcontrol.c:2867
__alloc_frozen_pages_noprof+0x18a/0x350 mm/page_alloc.c:5257
alloc_pages_mpol+0xb3/0x260 mm/mempolicy.c:2486
alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline]
alloc_pages_noprof+0x8f/0x130 mm/mempolicy.c:2577
vm_area_alloc_pages mm/vmalloc.c:3718 [inline]
__vmalloc_area_node mm/vmalloc.c:3863 [inline]
__vmalloc_node_range_noprof+0xa46/0x12b0 mm/vmalloc.c:4051
__kvmalloc_node_noprof+0x471/0x680 mm/slub.c:7164
ip_set_alloc+0x24/0x30 net/netfilter/ipset/ip_set_core.c:261
hash_netiface_create+0x282/0x740 net/netfilter/ipset/ip_set_hash_gen.h:1568
ip_set_create+0x3cf/0x970 net/netfilter/ipset/ip_set_core.c:1109
nfnetlink_rcv_msg+0x509/0x5d0 net/netfilter/nfnetlink.c:302
netlink_rcv_skb+0x123/0x220 net/netlink/af_netlink.c:2550
nfnetlink_rcv+0x167/0x1720 net/netfilter/nfnetlink.c:669
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x5c0/0x690 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x5c8/0x6f0 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x145/0x170 net/socket.c:742
____sys_sendmsg+0x31e/0x4a0 net/socket.c:2592
___sys_sendmsg+0x195/0x1e0 net/socket.c:2646
__sys_sendmsg net/socket.c:2678 [inline]
__do_sys_sendmsg net/socket.c:2683 [inline]
__se_sys_sendmsg net/socket.c:2681 [inline]
__x64_sys_sendmsg+0xd4/0x160 net/socket.c:2681
x64_sys_call+0x17ba/0x3000 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000001cf -> 0x00000000000001d0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 8167 Comm: syz.4.11146 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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