[syzbot] [perf?] WARNING in __free_event

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0a87d6bb6fd2 Merge tag 'powerpc-6.15-2' of git://git.kerne..
git tree: bpf-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1780f7b0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6631c78ce6cb228d
dashboard link: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15440be4580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12295404580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e5cffcf83e28/disk-0a87d6bb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/905e70de24af/vmlinux-0a87d6bb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5c28ed628313/bzImage-0a87d6bb.xz

The issue was bisected to:

commit 00b35530811f2aa3d7ceec2dbada80861c7632a8
Author: Eric Dumazet <edum...@google.com>
Date: Thu Feb 6 14:04:22 2025 +0000

batman-adv: adopt netdev_hold() / netdev_put()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10a7e94c580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=12a7e94c580000
console output: https://syzkaller.appspot.com/x/log.txt?x=14a7e94c580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ff3aa8...@syzkaller.appspotmail.com
Fixes: 00b35530811f ("batman-adv: adopt netdev_hold() / netdev_put()")

------------[ cut here ]------------
WARNING: CPU: 1 PID: 6031 at kernel/events/core.c:5572 __free_event+0x50f/0x620 kernel/events/core.c:5572
Modules linked in:
CPU: 1 UID: 0 PID: 6031 Comm: syz-executor189 Not tainted 6.14.0-syzkaller-g0a87d6bb6fd2 #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
RIP: 0010:__free_event+0x50f/0x620 kernel/events/core.c:5572
Code: ff 48 c7 c7 a0 0c df 8e e8 6e a5 a6 ff 43 0f b6 44 25 00 84 c0 0f 85 f5 00 00 00 41 80 26 ef e9 ea fc ff ff e8 d2 46 cb ff 90 <0f> 0b 90 42 80 3c 3b 00 0f 85 2d fe ff ff e9 30 fe ff ff e8 b9 46
RSP: 0018:ffffc9000461f858 EFLAGS: 00010293
RAX: ffffffff81f8104e RBX: 1ffff110089a873c RCX: ffff88802f5dda00
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000001
RBP: 0000000000000003 R08: ffffffff81f80e1b R09: 1ffff1100fc94b45
R10: dffffc0000000000 R11: ffffed100fc94b46 R12: ffff888044d439d8
R13: ffff888044d439e0 R14: 1ffff110089a873b R15: dffffc0000000000
FS: 00007f1a7f6516c0(0000) GS:ffff888125099000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1a7f743320 CR3: 000000003461c000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
inherit_event+0x190/0x9d0 kernel/events/core.c:14036
inherit_group kernel/events/core.c:14110 [inline]
inherit_task_group+0x18d/0x4f0 kernel/events/core.c:14177
perf_event_init_context kernel/events/core.c:14226 [inline]
perf_event_init_task+0x244/0x650 kernel/events/core.c:14295
copy_process+0x151e/0x3d10 kernel/fork.c:2403
kernel_clone+0x242/0x930 kernel/fork.c:2844
__do_sys_clone kernel/fork.c:2987 [inline]
__se_sys_clone kernel/fork.c:2971 [inline]
__x64_sys_clone+0x268/0x2e0 kernel/fork.c:2971
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1a7f6b98d9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1a7f651218 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f1a7f743338 RCX: 00007f1a7f6b98d9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000ab009400
RBP: 00007f1a7f743330 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1a7f710a94
R13: affffff7ffffffff R14: 0000200000000180 R15: 00000000ab009400
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: #syz test
Author: gshah...@gmail.com

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0bb21659e252..153ba622cfa0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -14016,6 +14016,9 @@ inherit_event(struct perf_event *parent_event,
if (IS_ERR(child_event))
return child_event;

+ get_ctx(child_ctx);
+ child_event->ctx = child_ctx;
+
pmu_ctx = find_get_pmu_context(child_event->pmu, child_ctx,
child_event);
if (IS_ERR(pmu_ctx)) {
free_event(child_event);
@@ -14037,8 +14040,6 @@ inherit_event(struct perf_event *parent_event,
return NULL;
}

- get_ctx(child_ctx);
-
/*
* Make the child state follow the state of the parent event,
* not its attr.disabled bit. We hold the parent's mutex,
@@ -14059,7 +14060,6 @@ inherit_event(struct perf_event *parent_event,
local64_set(&hwc->period_left, sample_period);
}

- child_event->ctx = child_ctx;
child_event->overflow_handler = parent_event->overflow_handler;
child_event->overflow_handler_context
= parent_event->overflow_handler_context;
--
2.43.0

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file kernel/events/core.c
patch: **** unexpected end of file in patch



Tested on:

commit: c9661394 selftests/bpf: Convert comma to semicolon
git tree: bpf-next

kernel config: https://syzkaller.appspot.com/x/.config?x=6631c78ce6cb228d
dashboard link: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3
compiler:

patch: https://syzkaller.appspot.com/x/patch.diff?x=144b2b4c580000

[syzbot]

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
unregister_netdevice: waiting for DEV to become free

unregister_netdevice: waiting for batadv0 to become free. Usage count = 3

Tested on:

commit: c9661394 selftests/bpf: Convert comma to semicolon
git tree: bpf-next

console output: https://syzkaller.appspot.com/x/log.txt?x=17df2b4c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f2054704dd53fb80
dashboard link: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3

compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=165f0d78580000

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: #syz test: git://git.kernel.dk/linux.git syztest
Author: gshah...@gmail.com

Move the get_ctx(child_ctx) call and the child_event->ctx assignment to
occur immediately after the child event is allocated. Ensure that
child_event->ctx is non-NULL before any subsequent error path within
inherit_event calls free_event(), satisfying the assumptions of the
cleanup code.

Reported-by: syzbot+ff3aa8...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3
Signed-off-by: Gabriel Shahrouzi <gshah...@gmail.com>
---
kernel/events/core.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: #syz test: git://git.kernel.dk/linux.git master

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 5fc31936081919a8572a3d644f3fbb258038f337

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+ff3aa8...@syzkaller.appspotmail.com
Tested-by: syzbot+ff3aa8...@syzkaller.appspotmail.com

Tested on:

commit: 626e6212 io_uring/kbuf: conditional schedule on buffer..
git tree: git://git.kernel.dk/linux.git syztest
console output: https://syzkaller.appspot.com/x/log.txt?x=12d587e4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=dd7fe622caa5926a

dashboard link: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=12a27404580000

Note: testing is done by a robot and is best-effort only.

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
unregister_netdevice: waiting for DEV to become free

unregister_netdevice: waiting for batadv0 to become free. Usage count = 3


Tested on:

commit: 4a1d8aba Merge tag 'riscv-for-linus-6.15-mw1' of git:/..
git tree: git://git.kernel.dk/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=147c8d78580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f2054704dd53fb80

dashboard link: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=124587e4580000

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+ff3aa8...@syzkaller.appspotmail.com
Tested-by: syzbot+ff3aa8...@syzkaller.appspotmail.com

Tested on:

commit: 5fc31936 Merge tag 'net-6.14-rc8' of git://git.kernel...
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=10f3e23f980000
kernel config: https://syzkaller.appspot.com/x/.config?x=5729e4e4ef1e3907

dashboard link: https://syzkaller.appspot.com/bug?extid=ff3aa851d46ab82953a3
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=17c587e4580000