syzbot


KCSAN: data-race in smc_poll / smc_switch_to_fallback (3)

Status: moderation: reported on 2026/03/05 11:37
Subsystems: smc
[Documentation on labels]
Reported-by: syzbot+824a4843a1b37c266c6d@syzkaller.appspotmail.com
First crash: 17d, last: 6d20h
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
52f4bf3c-1e80-45f1-be2a-1d5e449dbdaf repro KCSAN: data-race in smc_poll / smc_switch_to_fallback (3) 2026/03/07 08:37 2026/03/07 08:37 2026/03/07 08:45 31e9c887f7dc24e04b3ca70d0d54fc34141844b0
59628032-5c46-490e-831a-e8035b503aa9 assessment-kcsan Benign: ✅  Confident: ✅  KCSAN: data-race in smc_poll / smc_switch_to_fallback (3) 2026/02/23 14:47 2026/02/23 14:47 2026/02/23 14:50 305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in smc_poll / smc_switch_to_fallback smc 6 1 1156d 1094d 0/29 auto-obsoleted due to no activity on 2023/03/26 15:22
upstream KCSAN: data-race in smc_poll / smc_switch_to_fallback (2) smc 6 1 236d 236d 0/29 auto-obsoleted due to no activity on 2025/09/11 15:31

Sample crash report:
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
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/04 06:49 upstream 0031c06807cf 4180d919 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in smc_poll / smc_switch_to_fallback
2026/02/21 05:11 upstream a95f71ad3e2e 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in smc_poll / smc_switch_to_fallback
* Struck through repros no longer work on HEAD.