KCSAN: data-race in data_push_tail / uuid_string (7)

Status: moderation: reported on 2026/09/23 00:30
Subsystems: ext4
Labels: race:benign
[Documentation on labels]
Reported-by: syzbot+144e00d3b0af474fddfa@syzkaller.appspotmail.com
First crash: 2h33m, last: 2h33m
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
66818979 assessment-kcsan Benign: ✅ KCSAN: data-race in data_push_tail / uuid_string (7) 2026/09/23 00:33 2026/09/23 00:33 2026/09/23 01:19 5207b90e
Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in data_push_tail / uuid_string (3) ext4 6 1 886d 886d 0/29 auto-obsoleted due to no activity on 2024/05/24 03:21
upstream KCSAN: data-race in data_push_tail / uuid_string (6) race:benign prio:high ext4 6 2 88d 114d 0/29 auto-obsoleted due to no activity on 2026/08/21 12:55
upstream KCSAN: data-race in data_push_tail / uuid_string (4) ext4 6 1 681d 681d 0/29 auto-obsoleted due to no activity on 2025/01/05 15:54
upstream KCSAN: data-race in data_push_tail / uuid_string ext4 6 4 1095d 1174d 0/29 auto-obsoleted due to no activity on 2023/10/28 05:07
upstream KCSAN: data-race in data_push_tail / uuid_string (5) ext4 6 2 244d 264d 0/29 auto-obsoleted due to no activity on 2026/03/18 10:12
upstream KCSAN: data-race in data_push_tail / uuid_string (2) ext4 6 1 1024d 1020d 0/29 auto-obsoleted due to no activity on 2024/01/09 18:19

Sample crash report:
EXT4-fs error (device loop2): ext4_orphan_get:1403: inode #15: comm syz.2.2993: iget: bad i_size value: 38620345925642
loop2: lost file I/O error report for ino 15 type 5 pos 0x0 len 0x0 error -117
==================================================================
BUG: KCSAN: data-race in data_push_tail / uuid_string

write to 0xffffffff895d5570 of 1 bytes by task 6331 on cpu 1:
 string_nocheck lib/vsprintf.c:652 [inline]
 uuid_string+0x3ca/0x450 lib/vsprintf.c:1774
 pointer+0x3e2/0xc90 lib/vsprintf.c:2575
 vsnprintf+0x49e/0x8c0 lib/vsprintf.c:2953
 va_format lib/vsprintf.c:1725 [inline]
 pointer+0x844/0xc90 lib/vsprintf.c:2577
 vsnprintf+0x49e/0x8c0 lib/vsprintf.c:2953
 vscnprintf+0x41/0x90 lib/vsprintf.c:3018
 printk_sprint+0x30/0x2b0 kernel/printk/printk.c:2222
 vprintk_store+0x57f/0x910 kernel/printk/printk.c:2364
 vprintk_emit+0x1a4/0x610 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 __ext4_msg+0x1aa/0x1c0 fs/ext4/super.c:1001
 ext4_put_super+0x90/0x7c0 fs/ext4/super.c:1302
 generic_shutdown_super+0xee/0x220 fs/super.c:755
 kill_block_super+0x2d/0xb0 fs/super.c:1904
 ext4_kill_sb+0x42/0x80 fs/ext4/super.c:7527
 deactivate_locked_super+0x75/0x200 fs/super.c:589
 deactivate_super+0x9a/0xb0 fs/super.c:618
 cleanup_mnt+0x2c3/0x340 fs/namespace.c:1317
 __cleanup_mnt+0x19/0x20 fs/namespace.c:1324
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:70 [inline]
 exit_to_user_mode_loop+0x1e4/0x8c0 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:343 [inline]
 do_syscall_64+0x212/0x360 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff895d5570 of 8 bytes by task 16117 on cpu 0:
 data_make_reusable kernel/printk/printk_ringbuffer.c:608 [inline]
 data_push_tail+0x104/0x440 kernel/printk/printk_ringbuffer.c:693
 data_alloc+0x111/0x380 kernel/printk/printk_ringbuffer.c:1089
 prb_reserve+0x8e3/0xaf0 kernel/printk/printk_ringbuffer.c:1727
 vprintk_store+0x54e/0x910 kernel/printk/printk.c:2354
 vprintk_emit+0x1a4/0x610 kernel/printk/printk.c:2455
 vprintk_default+0x26/0x30 kernel/printk/printk.c:2494
 vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
 _printk+0x79/0xa0 kernel/printk/printk.c:2504
 fserror_report+0x3b8/0x500 fs/fserror.c:178
 fserror_report_file_metadata include/linux/fserror.h:61 [inline]
 __ext4_error_inode+0x177/0x3a0 fs/ext4/super.c:867
 __ext4_iget+0x1024/0x2360 fs/ext4/inode.c:-1
 ext4_orphan_get+0x157/0x410 fs/ext4/ialloc.c:1403
 ext4_orphan_cleanup+0x6a6/0xab0 fs/ext4/orphan.c:466
 __ext4_fill_super fs/ext4/super.c:5726 [inline]
 ext4_fill_super+0x33ea/0x37b0 fs/ext4/super.c:5855
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1873
 get_tree_bdev+0x1f/0x30 fs/super.c:1896
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5887
 vfs_get_tree+0x57/0x1d0 fs/super.c:1933
 fc_mount fs/namespace.c:1198 [inline]
 do_new_mount_fc fs/namespace.c:3772 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3848
 path_mount+0x4ad/0xb90 fs/namespace.c:4168
 do_mount fs/namespace.c:4181 [inline]
 __do_sys_mount fs/namespace.c:4397 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4374
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4374
 x64_sys_call+0xc3b/0x2550 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x3ffffffffffffc90 -> 0x000a2e302e303030

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16117 Comm: syz.2.2993 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================
EXT4-fs error (device loop2): ext4_orphan_get:1408: comm syz.2.2993: couldn't read orphan inode 15 (err -117)
loop2: lost filesystem error report for type 5 error -117
EXT4-fs (loop2): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
EXT4-fs error (device loop2): __ext4_iget:5592: inode #16: block 50331678: comm syz.2.2993: invalid block

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/23 00:29 upstream c4e9f74da438 5207b90e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in data_push_tail / uuid_string
* Struck through repros no longer work on HEAD.