linux-kernel - [syzbot] [smc?] KCSAN: data-race in smc_switch_to_fallback / sock

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Message-ID: <69858738.050a0220.3b3015.002e.GAE@google.com>
Date: Thu, 05 Feb 2026 22:16:24 -0800
From: syzbot <syzbot+198c20fde37cb9f6b0ac@...kaller.appspotmail.com>
To: alibuda@...ux.alibaba.com, davem@...emloft.net, dust.li@...ux.alibaba.com, 
	edumazet@...gle.com, guwen@...ux.alibaba.com, horms@...nel.org, 
	kuba@...nel.org, linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org, 
	linux-s390@...r.kernel.org, mjambigi@...ux.ibm.com, netdev@...r.kernel.org, 
	pabeni@...hat.com, sidraya@...ux.ibm.com, syzkaller-bugs@...glegroups.com, 
	tonylu@...ux.alibaba.com, wenjia@...ux.ibm.com
Subject: [syzbot] [smc?] KCSAN: data-race in smc_switch_to_fallback /
 sock_poll (2)

Hello,

syzbot found the following issue on:

HEAD commit:    5fd0a1df5d05 Merge tag 'v6.19rc8-smb3-client-fixes' of git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1070aa5a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=198c20fde37cb9f6b0ac
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a09cd69509c3/disk-5fd0a1df.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f218ec1eb157/vmlinux-5fd0a1df.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8549229eee91/bzImage-5fd0a1df.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+198c20fde37cb9f6b0ac@...kaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in smc_switch_to_fallback / sock_poll

write to 0xffff888127398c18 of 8 bytes by task 14369 on cpu 1:
 smc_switch_to_fallback+0x4ea/0x7e0 net/smc/af_smc.c:933
 smc_sendmsg+0xce/0x2f0 net/smc/af_smc.c:2797
 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+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

read to 0xffff888127398c18 of 8 bytes by task 14367 on cpu 0:
 sock_poll+0x27/0x240 net/socket.c:1427
 vfs_poll include/linux/poll.h:82 [inline]
 __io_arm_poll_handler+0x1ee/0xb80 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:1793
 io_issue_sqe+0x20b/0xc20 io_uring/io_uring.c:1816
 io_queue_sqe io_uring/io_uring.c:2043 [inline]
 io_submit_sqe io_uring/io_uring.c:2321 [inline]
 io_submit_sqes+0x78a/0x11b0 io_uring/io_uring.c:2435
 __do_sys_io_uring_enter io_uring/io_uring.c:3285 [inline]
 __se_sys_io_uring_enter+0x1bf/0x1c70 io_uring/io_uring.c:3224
 __x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:3224
 x64_sys_call+0x27e4/0x3000 arch/x86/include/generated/asm/syscalls_64.h:427
 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: 0xffff88811a6056c0 -> 0xffff88811a606080

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 14367 Comm: syz.8.3658 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


---
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