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KCSAN: data-race in do_sendfile / ksys_write (17)

Status: moderation: reported on 2026/02/23 09:50
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+1cf87899dfb5e587b1b0@syzkaller.appspotmail.com
First crash: 6d00h, last: 6d00h
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
0dc2341b-17f1-4b2b-bea8-238d8664da37 assessment-kcsan Benign: ❌  Confident: ✅  ❓ KCSAN: data-race in do_sendfile / ksys_write (17) 2026/02/23 14:19 2026/02/23 14:19 2026/02/23 14:31 305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9
▶ ▼ Similar bugs (16)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in do_sendfile / ksys_write (16) fs 6 1 676d 676d 0/29 auto-obsoleted due to no activity on 2024/05/28 12:59
upstream KCSAN: data-race in do_sendfile / ksys_write (5) fs 6 1 1867d 1867d 0/29 auto-closed as invalid on 2021/02/23 08:15
upstream KCSAN: data-race in do_sendfile / ksys_write (7) fs 6 3 1498d 1522d 0/29 auto-closed as invalid on 2022/02/27 04:59
upstream KCSAN: data-race in do_sendfile / ksys_write (8) fs 6 1 1457d 1457d 0/29 auto-closed as invalid on 2022/04/08 18:00
upstream KCSAN: data-race in do_sendfile / ksys_write (12) fs 6 2 987d 1000d 0/29 auto-obsoleted due to no activity on 2023/07/23 08:25
upstream KCSAN: data-race in do_sendfile / ksys_write (15) fs 6 1 736d 736d 0/29 auto-obsoleted due to no activity on 2024/03/29 14:30
upstream KCSAN: data-race in do_sendfile / ksys_write fs 6 1 2310d 2310d 0/29 closed as invalid on 2019/11/19 13:24
upstream KCSAN: data-race in do_sendfile / ksys_write (14) fs 6 2 812d 811d 0/29 auto-obsoleted due to no activity on 2024/01/14 07:58
upstream KCSAN: data-race in do_sendfile / ksys_write (13) fs 6 5 880d 937d 0/29 auto-obsoleted due to no activity on 2023/11/07 08:57
upstream KCSAN: data-race in do_sendfile / ksys_write (2) fs 6 2 2193d 2255d 0/29 auto-closed as invalid on 2020/05/08 04:57
upstream KCSAN: data-race in do_sendfile / ksys_write (6) fs 6 1 1799d 1799d 0/29 auto-closed as invalid on 2021/05/17 10:56
upstream KCSAN: data-race in do_sendfile / ksys_write (4) fs 6 1 1902d 1902d 0/29 auto-closed as invalid on 2021/01/18 19:47
upstream KCSAN: data-race in do_sendfile / ksys_write (10) fs 6 1 1316d 1316d 0/29 auto-closed as invalid on 2022/08/27 13:39
upstream KCSAN: data-race in do_sendfile / ksys_write (3) fs 6 1 1976d 1976d 0/29 auto-closed as invalid on 2020/11/06 02:13
upstream KCSAN: data-race in do_sendfile / ksys_write (9) fs 6 2 1398d 1401d 0/29 auto-closed as invalid on 2022/06/06 18:20
upstream KCSAN: data-race in do_sendfile / ksys_write (11) fs 6 1 1249d 1249d 0/29 auto-obsoleted due to no activity on 2022/11/02 18:18

Sample crash report:
==================================================================
BUG: KCSAN: data-race in do_sendfile / ksys_write

write to 0xffff88811b0e52b0 of 8 bytes by task 27124 on cpu 0:
 ksys_write+0x11c/0x1a0 fs/read_write.c:742
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 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

write to 0xffff88811b0e52b0 of 8 bytes by task 27147 on cpu 1:
 do_sendfile+0x40d/0x650 fs/read_write.c:1386
 __do_sys_sendfile64 fs/read_write.c:1433 [inline]
 __se_sys_sendfile64 fs/read_write.c:1419 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1419
 x64_sys_call+0x2dc4/0x3020 arch/x86/include/generated/asm/syscalls_64.h:41
 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: 0x0000000000000000 -> 0x0000000000000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 27147 Comm: syz.7.6128 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 (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/23 09:50 upstream 6de23f81a5e0 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in do_sendfile / ksys_write
* Struck through repros no longer work on HEAD.