syzbot


KCSAN: data-race in _copy_to_iter / kmmpd (4)

Status: moderation: reported on 2026/05/05 04:13
Subsystems: ext4
[Documentation on labels]
Reported-by: syzbot+7d61c0a6b5a53cb919e2@syzkaller.appspotmail.com
First crash: 1d05h, last: 1d05h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
b3478bb0-165b-427f-ae5f-55a46ab26274 assessment-kcsan Benign: ✅ Confident: ✅ KCSAN: data-race in _copy_to_iter / kmmpd (4) 2026/05/05 04:13 2026/05/05 04:13 2026/05/05 04:36 fb79c7648187955b4a207be44fe337d66e9538e9
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in _copy_to_iter / kmmpd ext4 6 1 621d 621d 0/29 auto-obsoleted due to no activity on 2024/09/27 00:36
upstream KCSAN: data-race in _copy_to_iter / kmmpd (2) ext4 6 1 300d 300d 0/29 auto-obsoleted due to no activity on 2025/09/03 21:37
upstream KCSAN: data-race in _copy_to_iter / kmmpd (3) ext4 block 6 3 142d 175d 0/29 auto-obsoleted due to no activity on 2026/02/08 18:21

Sample crash report:
==================================================================
BUG: KCSAN: data-race in _copy_to_iter / kmmpd

write to 0xffff88812683f008 of 8 bytes by task 18178 on cpu 1:
 kmmpd+0xb7/0x670 fs/ext4/mmp.c:149
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff88812683f000 of 512 bytes by task 15022 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:130 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0x130/0xea0 lib/iov_iter.c:197
 copy_page_to_iter+0x178/0x210 lib/iov_iter.c:374
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 filemap_read+0x407/0xa10 mm/filemap.c:2857
 blkdev_read_iter+0x22d/0x2e0 block/fops.c:855
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x6c0/0x7f0 fs/read_write.c:574
 ksys_read+0xdc/0x1a0 fs/read_write.c:717
 __do_sys_read fs/read_write.c:726 [inline]
 __se_sys_read fs/read_write.c:724 [inline]
 __x64_sys_read+0x40/0x50 fs/read_write.c:724
 x64_sys_call+0x2886/0x3020 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 15022 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/05 04:12 upstream c7e4e4d5f7dc a898ba9c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / kmmpd
* Struck through repros no longer work on HEAD.