syzbot


WARNING in bpf_probe_read_user

Status: upstream: reported C repro on 2023/11/04 18:36
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+9fef5b251417ebc881c0@syzkaller.appspotmail.com
First crash: 667d, last: 9m
Fix commit to backport (bisect log) :
tree: upstream
commit d319f344561de23e810515d109c7278919bff7b0
Author: Alexei Starovoitov <ast@kernel.org>
Date: Mon Apr 10 17:43:44 2023 +0000

  mm: Fix copy_from_user_nofault().

  
Bug presence (2)
Date Name Commit Repro Result
2023/11/05 linux-5.15.y (ToT) 12952a23a5da C [report] WARNING in bpf_probe_read_user
2023/11/05 upstream (ToT) aea6bf908d73 C Didn't crash
Fix bisection attempts (1)
Created Duration User Patch Repo Result
2023/11/05 20:34 4h18m fix candidate upstream OK (1) job log

Sample crash report:
------------[ cut here ]------------
WARNING: CPU: 1 PID: 20 at mm/maccess.c:226 copy_from_user_nofault+0x160/0x1c0 mm/maccess.c:226
Modules linked in:
CPU: 1 PID: 20 Comm: ksoftirqd/1 Not tainted 5.15.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:copy_from_user_nofault+0x160/0x1c0 mm/maccess.c:226
Code: 24 45 31 f6 31 ff 89 de e8 ed f7 d8 ff 85 db 48 c7 c0 f2 ff ff ff 49 0f 44 c6 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 70 f4 d8 ff <0f> 0b e9 1c ff ff ff 44 89 e1 80 e1 07 80 c1 03 38 c1 0f 8c ea fe
RSP: 0018:ffffc90000da78a8 EFLAGS: 00010246
RAX: ffffffff819ecfb0 RBX: 0000000000000008 RCX: ffff88813fe60000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: dffffc0000000000 R09: fffffbfff1ff6e19
R10: fffffbfff1ff6e19 R11: 1ffffffff1ff6e18 R12: ffff88813fe61788
R13: 1ffff920001b4f24 R14: ffffc90000da7908 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055555fda6808 CR3: 000000007cb9d000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 bpf_probe_read_user_common kernel/trace/bpf_trace.c:157 [inline]
 ____bpf_probe_read_user kernel/trace/bpf_trace.c:166 [inline]
 bpf_probe_read_user+0x26/0x70 kernel/trace/bpf_trace.c:163
 </TASK>
Kernel panic - not syncing: kernel: panic_on_warn set ...
CPU: 1 PID: 20 Comm: ksoftirqd/1 Not tainted 5.15.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 panic+0x2c9/0x7f0 kernel/panic.c:309
 check_panic_on_warn kernel/panic.c:229 [inline]
 __warn+0x248/0x2b0 kernel/panic.c:680
 report_bug+0x1b7/0x2e0 lib/bug.c:199
 handle_bug+0x3a/0x70 arch/x86/kernel/traps.c:239
 exc_invalid_op+0x16/0x40 arch/x86/kernel/traps.c:259
 asm_exc_invalid_op+0x16/0x20 arch/x86/include/asm/idtentry.h:604
RIP: 0010:copy_from_user_nofault+0x160/0x1c0 mm/maccess.c:226
Code: 24 45 31 f6 31 ff 89 de e8 ed f7 d8 ff 85 db 48 c7 c0 f2 ff ff ff 49 0f 44 c6 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 70 f4 d8 ff <0f> 0b e9 1c ff ff ff 44 89 e1 80 e1 07 80 c1 03 38 c1 0f 8c ea fe
RSP: 0018:ffffc90000da78a8 EFLAGS: 00010246
RAX: ffffffff819ecfb0 RBX: 0000000000000008 RCX: ffff88813fe60000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: dffffc0000000000 R09: fffffbfff1ff6e19
R10: fffffbfff1ff6e19 R11: 1ffffffff1ff6e18 R12: ffff88813fe61788
R13: 1ffff920001b4f24 R14: ffffc90000da7908 R15: 0000000000000000
 bpf_probe_read_user_common kernel/trace/bpf_trace.c:157 [inline]
 ____bpf_probe_read_user kernel/trace/bpf_trace.c:166 [inline]
 bpf_probe_read_user+0x26/0x70 kernel/trace/bpf_trace.c:163
 </TASK>
Kernel Offset: disabled
Rebooting in 86400 seconds..

Crashes (103636):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/25 11:57 linux-5.15.y c79648372d02 bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/08/25 04:21 linux-5.15.y c79648372d02 bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/08/22 08:06 linux-5.15.y c79648372d02 bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/18 10:28 linux-5.15.y c79648372d02 1804e95e .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/14 17:15 linux-5.15.y c79648372d02 5d8c2ac2 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/13 01:46 linux-5.15.y c79648372d02 22ec1469 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/12 08:51 linux-5.15.y c79648372d02 c06e8995 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/11 17:13 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/10 13:55 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/10 11:01 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/10 09:19 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/09 21:21 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/09 12:03 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/09 07:01 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/09 06:31 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/09 06:02 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/09 04:27 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/08 22:49 linux-5.15.y c79648372d02 32a0e5ed .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/07 13:20 linux-5.15.y c79648372d02 04cffc22 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/07 12:12 linux-5.15.y c79648372d02 04cffc22 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/07 09:46 linux-5.15.y c79648372d02 9a42d6b1 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/07 09:16 linux-5.15.y c79648372d02 9a42d6b1 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/07 07:19 linux-5.15.y c79648372d02 9a42d6b1 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 21:31 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 20:57 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 20:13 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 19:33 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 18:52 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 17:49 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 11:07 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 10:25 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 09:35 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 08:37 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/06 06:03 linux-5.15.y c79648372d02 ffe1dd46 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/05 05:21 linux-5.15.y c79648372d02 f5bcc8dc .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/05 04:40 linux-5.15.y c79648372d02 f5bcc8dc .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/03 22:21 linux-5.15.y c79648372d02 7368264b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/03 14:51 linux-5.15.y c79648372d02 7368264b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/03 04:18 linux-5.15.y c79648372d02 7368264b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/01 14:41 linux-5.15.y c79648372d02 40127d41 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2023/11/04 23:31 linux-5.15.y 12952a23a5da 500bfdc4 .config console log report syz C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 14:30 linux-5.15.y 01879f56bdde 96a211bc .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 12:41 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 11:35 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 10:25 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/02 09:37 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 08:36 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 05:44 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 04:33 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 03:32 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/02 02:14 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 01:19 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/02 00:18 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 22:37 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 21:37 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 20:24 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 19:30 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 18:30 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 18:10 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 16:57 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 15:45 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 14:57 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 14:31 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 12:48 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 11:47 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 10:36 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 09:34 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 09:04 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 08:48 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 05:42 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 04:14 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 04:09 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/09/01 03:06 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 01:56 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 01:24 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 01:24 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/09/01 00:23 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/31 23:22 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/31 23:12 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/31 21:13 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/08/31 20:25 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/08/31 20:23 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/08/31 19:21 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
2025/08/31 15:53 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2025/08/31 15:25 linux-5.15.y 01879f56bdde 807a3b61 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in bpf_probe_read_user
2023/11/04 18:36 linux-5.15.y 12952a23a5da 500bfdc4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in bpf_probe_read_user
* Struck through repros no longer work on HEAD.