KCSAN: data-race in data_alloc / data_push_tail (4)

Status: moderation: reported on 2026/10/02 03:22
Subsystems: audit
Labels: race:benign
[Documentation on labels]
Reported-by: syzbot+8324b8fd984b86905a66@syzkaller.appspotmail.com
First crash: 5h13m, last: 5h13m
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
fbcc89ea assessment-kcsan Benign: ✅ ❓ KCSAN: data-race in data_alloc / data_push_tail (4) 2026/10/02 03:22 2026/10/02 03:22 2026/10/02 03:59 6d32eb1f
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in data_alloc / data_push_tail (3) prio:low ext4 block 6 75 69d 754d 0/29 auto-obsoleted due to no activity on 2026/09/18 22:44
upstream KCSAN: data-race in data_alloc / data_push_tail (2) batman 6 44 800d 943d 0/29 auto-obsoleted due to no activity on 2024/08/28 06:32
upstream KCSAN: data-race in data_alloc / data_push_tail ext4 6 94 1254d 1717d 0/29 auto-obsoleted due to no activity on 2023/05/31 17:30

Sample crash report:
 <TASK>
 __dump_stack+0x1d/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x95/0xd0 lib/dump_stack.c:120
==================================================================
BUG: KCSAN: data-race in data_alloc / data_push_tail

write to 0xffffffff895bdcd8 of 8 bytes by task 29 on cpu 0:
 data_alloc+0x240/0x380 kernel/printk/printk_ringbuffer.c:1116
 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
 kauditd_printk_skb kernel/audit.c:588 [inline]
 kauditd_hold_skb+0x1b1/0x1c0 kernel/audit.c:623
 kauditd_send_queue+0x275/0x2d0 kernel/audit.c:808
 kauditd_thread+0x439/0x660 kernel/audit.c:932
 kthread+0x223/0x270 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 0xffffffff895bdcd8 of 8 bytes by task 8433 on cpu 1:
 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
 printk_stack_address arch/x86/kernel/dumpstack.c:70 [inline]
 __show_trace_log_lvl+0x460/0x560 arch/x86/kernel/dumpstack.c:282
 __dump_stack+0x1d/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x95/0xd0 lib/dump_stack.c:120
 dump_stack+0x15/0x1b lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x262/0x280 lib/fault-inject.c:174
 should_failslab+0x8c/0xb0 mm/failslab.c:46
 slab_pre_alloc_hook mm/slub.c:4638 [inline]
 slab_alloc_node mm/slub.c:4974 [inline]
 __kmalloc_cache_noprof+0x7a/0x400 mm/slub.c:5559
 _kmalloc_noprof include/linux/slab.h:991 [inline]
 _kzalloc_noprof include/linux/slab.h:1312 [inline]
 ramfs_init_fs_context+0x31/0x80 fs/ramfs/inode.c:301
 alloc_fs_context+0x490/0x570 fs/fs_context.c:295
 fs_context_for_mount+0x22/0x30 fs/fs_context.c:309
 __do_sys_fsopen fs/fsopen.c:142 [inline]
 __se_sys_fsopen+0xa0/0x1e0 fs/fsopen.c:120
 __x64_sys_fsopen+0x31/0x40 fs/fsopen.c:120
 x64_sys_call+0x1f0f/0x2550 arch/x86/include/generated/asm/syscalls_64.h:431
 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: 0x3fffffffffffe20e -> 0x3fffffffffffee22

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 8433 Comm: syz.2.1462 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
==================================================================
 dump_stack+0x15/0x1b lib/dump_stack.c:129
 fail_dump lib/fault-inject.c:73 [inline]
 should_fail_ex+0x262/0x280 lib/fault-inject.c:174
 should_failslab+0x8c/0xb0 mm/failslab.c:46
 slab_pre_alloc_hook mm/slub.c:4638 [inline]
 slab_alloc_node mm/slub.c:4974 [inline]
 __kmalloc_cache_noprof+0x7a/0x400 mm/slub.c:5559
 _kmalloc_noprof include/linux/slab.h:991 [inline]
 _kzalloc_noprof include/linux/slab.h:1312 [inline]
 ramfs_init_fs_context+0x31/0x80 fs/ramfs/inode.c:301
 alloc_fs_context+0x490/0x570 fs/fs_context.c:295
 fs_context_for_mount+0x22/0x30 fs/fs_context.c:309
 __do_sys_fsopen fs/fsopen.c:142 [inline]
 __se_sys_fsopen+0xa0/0x1e0 fs/fsopen.c:120
 __x64_sys_fsopen+0x31/0x40 fs/fsopen.c:120
 x64_sys_call+0x1f0f/0x2550 arch/x86/include/generated/asm/syscalls_64.h:431
 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
RIP: 0033:0x7f76623be159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7660e17028 EFLAGS: 00000246 ORIG_RAX: 00000000000001ae
RAX: ffffffffffffffda RBX: 00007f7662645fa0 RCX: 00007f76623be159
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000180
RBP: 00007f766245506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7662646038 R14: 00007f7662645fa0 R15: 00007ffe4cb0afd8
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/02 03:22 upstream ce1e0223d8ad 6d32eb1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in data_alloc / data_push_tail
* Struck through repros no longer work on HEAD.