[moderation] [smc?] KCSAN: data-race in smc_poll / smc_switch_to_fallback (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0031c06807cf Merge tag 'cgroup-for-7.0-rc2-fixes' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=177b1b5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6b32b22d8934c136
dashboard link: https://syzkaller.appspot.com/bug?extid=824a4843a1b37c266c6d
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [ali...@linux.alibaba.com da...@davemloft.net dus...@linux.alibaba.com edum...@google.com gu...@linux.alibaba.com ho...@kernel.org ku...@kernel.org linux-...@vger.kernel.org linux...@vger.kernel.org linux...@vger.kernel.org mjam...@linux.ibm.com net...@vger.kernel.org pab...@redhat.com sid...@linux.ibm.com ton...@linux.alibaba.com wen...@linux.ibm.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4e24462b7c3a/disk-0031c068.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/de3ed600677d/vmlinux-0031c068.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b339fd8fe415/bzImage-0031c068.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+824a48...@syzkaller.appspotmail.com

SELinux: inode_doinit_use_xattr: getxattr returned 5 for dev=loop6 ino=12
SELinux: inode_doinit_use_xattr: getxattr returned 5 for dev=loop6 ino=13
==================================================================
BUG: KCSAN: data-race in smc_poll / smc_switch_to_fallback

write to 0xffff88811bf2d94d of 1 bytes by task 8404 on cpu 1:
smc_switch_to_fallback+0x5a/0x7f0 net/smc/af_smc.c:929
smc_sendmsg+0xce/0x2f0 net/smc/af_smc.c:2799
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg net/socket.c:742 [inline]
____sys_sendmsg+0x5af/0x600 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+0x194c/0x3020 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811bf2d94d of 1 bytes by task 8390 on cpu 0:
smc_poll+0x4a/0x530 net/smc/af_smc.c:2885
sock_poll+0x21c/0x240 net/socket.c:1443
vfs_poll include/linux/poll.h:82 [inline]
__io_arm_poll_handler+0x1ec/0xc30 io_uring/poll.c:581
io_poll_add+0x69/0xf0 io_uring/poll.c:899
__io_issue_sqe+0xfd/0x2d0 io_uring/io_uring.c:1384
io_issue_sqe+0x206/0xc00 io_uring/io_uring.c:1407
io_queue_sqe io_uring/io_uring.c:1634 [inline]
io_submit_sqe io_uring/io_uring.c:1920 [inline]
io_submit_sqes+0x7fb/0x1270 io_uring/io_uring.c:2043
__do_sys_io_uring_enter io_uring/io_uring.c:2603 [inline]
__se_sys_io_uring_enter+0x1c9/0xf50 io_uring/io_uring.c:2538
__x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:2538
x64_sys_call+0x1e16/0x3020 arch/x86/include/generated/asm/syscalls_64.h:427
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 8390 Comm: syz.6.1361 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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