linux-kernel - [WARNING] WARNING in x86_pmu_stop() (arch/x86/events/core.c:1624) triggered by syzkaller repro

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Message-ID:
	<PS1PPF7E1D7501F6302C4D63E37AB0D5FC5AB98A@PS1PPF7E1D7501F.apcprd02.prod.outlook.com>
Date: Wed, 4 Feb 2026 13:11:41 +0000
From: 是参差 <shicenci@...il.com>
To: "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peterz@...radead.org" <peterz@...radead.org>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "bp@...en8.de" <bp@...en8.de>,
	"acme@...nel.org" <acme@...nel.org>
Subject: [WARNING] WARNING in x86_pmu_stop() (arch/x86/events/core.c:1624)
 triggered by syzkaller repro

Hi,
I’m reporting a reproducible WARNING observed in the x86 perf PMU stop path.
The WARNING is triggered by a syzkaller C reproducer that performs multiple perf_event_open() calls with high-frequency sampling settings and then exercises a workload that heavily hits perf/tracepoint paths (e.g., sched tracepoints). The kernel hits a WARN in x86_pmu_stop() while handling perf event throttling/overflow.
The WARNING report points to:
WARNING: arch/x86/events/core.c:1624 at x86_pmu_stop+0x247/0x260, CPU#0: syz.2.7419/25339
Call trace (trimmed to the perf-relevant part):
perf_event_throttle.part.0
__perf_event_account_interrupt
__perf_event_overflow
perf_swevent_overflow
perf_swevent_event
perf_tp_event
perf_trace_run_bpf_submit
perf_trace_sched_stat_runtime
...
This suggests a possible state-machine inconsistency or corner-case interaction between the perf throttling/overflow handling and the x86 PMU stop path (x86_pmu_stop()), potentially triggered by an unusual perf_event_attr combination and high event rate.
Reproducer:
C reproducer: https://pastebin.com/raw/t9u91hQf
console output: https://pastebin.com/raw/XUw5zuQg
kernel config: https://pastebin.com/raw/dP93yBLn
Kernel:
git tree: torvalds/linux
kernel version: 6.19.0-rc7 #1 VOLUNTARY (QEMU Ubuntu 24.10)
HEAD commit:63804fed149a6750ffd28610c5c1c98cce6bd377



EXT4-fs (loop2): mounting ext3 file system using the ext4 subsystem
EXT4-fs (loop2): 1 truncate cleaned up
EXT4-fs (loop2): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
------------[ cut here ]------------
WARNING: arch/x86/events/core.c:1624 at x86_pmu_stop+0x247/0x260 arch/x86/events/core.c:1624, CPU#0: syz.2.7419/25339
CPU: 0 UID: 0 PID: 25339 Comm: syz.2.7419 Not tainted 6.19.0-rc7 #1 VOLUNTARY 
Hardware name: QEMU Ubuntu 24.10 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:x86_pmu_stop+0x247/0x260 arch/x86/events/core.c:1624
Code: 4c 89 ef e8 9b 59 6e 00 e9 48 ff ff ff 4c 89 ef e8 2e 5a 6e 00 eb 85 4c 89 e7 e8 84 59 6e 00 e9 83 fe ff ff e8 6a 99 3e 00 90 <0f> 0b 90 e9 44 ff ff ff 4c 89 e7 e8 69 59 6e 00 eb 96 0f 1f 80 00
RSP: 0018:ffff88800bebe868 EFLAGS: 00010012
RAX: 000000000000797b RBX: ffff888010488000 RCX: ffffc90000390000
RDX: 0000000000080000 RSI: ffff88802e495640 RDI: 0000000000000002
RBP: 0000000000000000 R08: ffffffff87073701 R09: ffffffff8120c1a6
R10: 0000000000000001 R11: ffffffff86e3a6c7 R12: 0000000000000001
R13: ffff8880104881f8 R14: 0000000000000001 R15: 0000000000000000
FS:  00007f99e6c976c0(0000) GS:0000000000000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000002000 CR3: 000000005f659000 CR4: 0000000000350ef0
DR0: 0000200000000080 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <TASK>
 perf_event_throttle.part.0+0x89/0xf0 kernel/events/core.c:2682
 perf_event_throttle kernel/events/core.c:2678 [inline]
 perf_event_throttle_group kernel/events/core.c:2700 [inline]
 __perf_event_account_interrupt+0x2a6/0x430 kernel/events/core.c:10258
 __perf_event_overflow+0xb6/0xa00 kernel/events/core.c:10405
 perf_swevent_overflow+0xac/0x150 kernel/events/core.c:10545
 perf_swevent_event+0x14d/0x2e0 kernel/events/core.c:10583
 perf_tp_event+0x3b7/0x810 kernel/events/core.c:11090
 perf_trace_run_bpf_submit+0xef/0x180 kernel/events/core.c:11014
 do_perf_trace_sched_stat_runtime include/trace/events/sched.h:553 [inline]
 perf_trace_sched_stat_runtime+0x360/0x680 include/trace/events/sched.h:553
 __do_trace_sched_stat_runtime include/trace/events/sched.h:576 [inline]
 trace_sched_stat_runtime include/trace/events/sched.h:576 [inline]
 update_se+0x39b/0x480 kernel/sched/fair.c:1159
 update_curr+0x71/0x450 kernel/sched/fair.c:1209
 put_prev_entity+0x97/0x1b0 kernel/sched/fair.c:5504
 pick_next_task_fair+0xf7e/0x17b0 kernel/sched/fair.c:8949
 __pick_next_task kernel/sched/core.c:5890 [inline]
 pick_next_task kernel/sched/core.c:6426 [inline]
 __schedule+0x740/0x1df0 kernel/sched/core.c:6809
 preempt_schedule_common kernel/sched/core.c:7051 [inline]
 __cond_resched+0x45/0x70 kernel/sched/core.c:7378
 mutex_lock+0x75/0xe0 kernel/locking/mutex.c:287
 ext4_mb_group_or_file fs/ext4/mballoc.c:5886 [inline]
 ext4_mb_initialize_context+0x85e/0xcf0 fs/ext4/mballoc.c:5930
 ext4_mb_new_blocks+0x603/0x3fc0 fs/ext4/mballoc.c:6304
 ext4_alloc_branch fs/ext4/indirect.c:340 [inline]
 ext4_ind_map_blocks+0x1635/0x20c0 fs/ext4/indirect.c:635
 ext4_map_create_blocks fs/ext4/inode.c:615 [inline]
 ext4_map_blocks+0xb51/0x1350 fs/ext4/inode.c:816
 _ext4_get_block+0x1bb/0x550 fs/ext4/inode.c:916
 ext4_block_write_begin+0x88a/0x1040 fs/ext4/inode.c:1203
 ext4_write_begin+0x75f/0x11d0 fs/ext4/inode.c:1364
 generic_perform_write+0x37d/0x800 mm/filemap.c:4314
 ext4_buffered_write_iter+0x11a/0x430 fs/ext4/file.c:299
 ext4_file_write_iter+0x560/0x1790 fs/ext4/file.c:723
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write fs/read_write.c:686 [inline]
 vfs_write+0xa66/0xe30 fs/read_write.c:666
 ksys_write+0x120/0x240 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xa9/0x320 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7f99e822ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f99e6c97038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f99e8465fa0 RCX: 00007f99e822ebe9
RDX: 000000000208e24b RSI: 0000200000000340 RDI: 000000000000000a
RBP: 00007f99e82b1e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f99e8466038 R14: 00007f99e8465fa0 R15: 00007ffc60f336c8
 </TASK>
---[ end trace 0000000000000000 ]---

Thanks