Re: [syzbot] [trace?] WARNING in trace_rb_cpu_prepare

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    28924df2a08f Merge tag 'perf-tools-fixes-for-v7.3-2026-09-..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15761af9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b454dc6b1b7acd30
dashboard link: https://syzkaller.appspot.com/bug?extid=fbe07bcf949966f3c00f
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ea2af9580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10eb3af9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dec945b3d75e/disk-28924df2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4e41f1bc0876/vmlinux-28924df2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ec9e83ddda2c/bzImage-28924df2.xz

Bisection is inconclusive: the first bad commit could be any of:

6a80838814ee tracing: Add show_event_triggers to expose active event triggers
729757b96a66 tracing: Add show_event_filters to expose active event filters
e4ef389e761b tracing: Check the return value of tracing_update_buffers()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11d7d4f9580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fbe07bcf949966f3c00f@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
failed to allocate ring buffer on CPU 1
WARNING: kernel/trace/ring_buffer.c:8103 at trace_rb_cpu_prepare+0x330/0x3c0 kernel/trace/ring_buffer.c:8102, CPU#0: syz.2.31/6050
Modules linked in:
CPU: 0 UID: 0 PID: 6050 Comm: syz.2.31 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:trace_rb_cpu_prepare+0x332/0x3c0 kernel/trace/ring_buffer.c:8102
Code: 08 f0 48 0f ab 03 31 c0 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 87 2e fc ff 48 8d 3d 40 36 eb 0d 89 ee <67> 48 0f b9 3a b8 f4 ff ff ff eb d2 e8 6d 2e fc ff e9 ef fe ff ff
RSP: 0018:ffffc90004a377d0 EFLAGS: 00010293
RAX: ffffffff81ca5f89 RBX: dffffc0000000000 RCX: ffff888027b3be80
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff8fb595d0
RBP: 0000000000000001 R08: ffffffff8fb1e77f R09: 1ffffffff1f63cef
R10: dffffc0000000000 R11: fffffbfff1f63cf0 R12: 0000000000000000
R13: ffff88803e2a2908 R14: ffff88805d68b0a0 R15: 0000000000000000
FS:  00007f1a0c90e6c0(0000) GS:ffff888125bd1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555867aea68 CR3: 000000002b852000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 cpuhp_invoke_callback+0x498/0x810 kernel/cpu.c:204
 cpuhp_issue_call+0x3f0/0x750 kernel/cpu.c:-1
 __cpuhp_state_add_instance_cpuslocked+0x225/0x560 kernel/cpu.c:2423
 __cpuhp_state_add_instance+0x25/0x40 kernel/cpu.c:2444
 cpuhp_state_add_instance include/linux/cpuhotplug.h:383 [inline]
 alloc_buffer+0x188f/0x1d70 kernel/trace/ring_buffer.c:2917
 __ring_buffer_alloc+0x2c/0x40 kernel/trace/ring_buffer.c:2959
 allocate_trace_buffer+0x1d2/0x950 kernel/trace/trace.c:8465
 allocate_trace_buffers kernel/trace/trace.c:8498 [inline]
 trace_array_create_systems+0x590/0xe60 kernel/trace/trace.c:8676
 trace_array_create kernel/trace/trace.c:8719 [inline]
 instance_mkdir+0xd5/0x140 kernel/trace/trace.c:8734
 tracefs_syscall_mkdir+0x11a/0x190 fs/tracefs/inode.c:121
 vfs_mkdir+0x408/0x620 fs/namei.c:5410
 filename_mkdirat+0x289/0x520 fs/namei.c:5443
 __do_sys_mkdirat fs/namei.c:5464 [inline]
 __se_sys_mkdirat+0x35/0x150 fs/namei.c:5461
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1a0d2ae159
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:00007f1a0c90e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007f1a0d535fa0 RCX: 00007f1a0d2ae159
RDX: 00000000000001ff RSI: 0000200000000140 RDI: ffffffffffffff9c
RBP: 00007f1a0d345024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1a0d536038 R14: 00007f1a0d535fa0 R15: 00007ffc0a111b18
 </TASK>
----------------
Code disassembly (best guess):
   0:	08 f0                	or     %dh,%al
   2:	48 0f ab 03          	bts    %rax,(%rbx)
   6:	31 c0                	xor    %eax,%eax
   8:	48 83 c4 30          	add    $0x30,%rsp
   c:	5b                   	pop    %rbx
   d:	41 5c                	pop    %r12
   f:	41 5d                	pop    %r13
  11:	41 5e                	pop    %r14
  13:	41 5f                	pop    %r15
  15:	5d                   	pop    %rbp
  16:	c3                   	ret
  17:	cc                   	int3
  18:	cc                   	int3
  19:	cc                   	int3
  1a:	cc                   	int3
  1b:	cc                   	int3
  1c:	e8 87 2e fc ff       	call   0xfffc2ea8
  21:	48 8d 3d 40 36 eb 0d 	lea    0xdeb3640(%rip),%rdi        # 0xdeb3668
  28:	89 ee                	mov    %ebp,%esi
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	b8 f4 ff ff ff       	mov    $0xfffffff4,%eax
  34:	eb d2                	jmp    0x8
  36:	e8 6d 2e fc ff       	call   0xfffc2ea8
  3b:	e9 ef fe ff ff       	jmp    0xffffff2f


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