linux-kernel - Re: [syzbot] [bpf?] WARNING in bpf_bprintf

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Message-ID: <68f7723f.050a0220.346f24.0015.GAE@google.com>
Date: Tue, 21 Oct 2025 04:45:03 -0700
From: syzbot <syzbot+b0cff308140f79a9c4cb@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, listout@...tout.xyz, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bpf?] WARNING in bpf_bprintf_prepare (3)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: bad unlock balance in bpf_test_timer_leave

=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.2.19/6466 is trying to release lock (rcu_read_lock) at:
[<ffffffff896fd470>] rcu_lock_release include/linux/rcupdate.h:341 [inline]
[<ffffffff896fd470>] rcu_read_unlock include/linux/rcupdate.h:897 [inline]
[<ffffffff896fd470>] bpf_test_timer_leave+0x1d0/0x290 net/bpf/test_run.c:48
but there are no more locks to release!

other info that might help us debug this:
no locks held by syz.2.19/6466.

stack backtrace:
CPU: 1 UID: 0 PID: 6466 Comm: syz.2.19 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_unlock_imbalance_bug+0xdc/0xf0 kernel/locking/lockdep.c:5298
 __lock_release kernel/locking/lockdep.c:5527 [inline]
 lock_release+0x212/0x3e0 kernel/locking/lockdep.c:5889
 rcu_lock_release include/linux/rcupdate.h:341 [inline]
 rcu_read_unlock include/linux/rcupdate.h:897 [inline]
 bpf_test_timer_leave+0x1dc/0x290 net/bpf/test_run.c:48
 bpf_test_timer_continue+0x244/0x320 net/bpf/test_run.c:74
 bpf_prog_test_run_flow_dissector+0x39c/0x5c0 net/bpf/test_run.c:1417
 bpf_prog_test_run+0x2c7/0x340 kernel/bpf/syscall.c:4688
 __sys_bpf+0x562/0x860 kernel/bpf/syscall.c:6167
 __do_sys_bpf kernel/bpf/syscall.c:6259 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6257 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6257
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa2f6f8efc9
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:00007fa2f7e1c038 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fa2f71e5fa0 RCX: 00007fa2f6f8efc9
RDX: 0000000000000050 RSI: 0000200000000180 RDI: 000000000000000a
RBP: 00007fa2f7011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa2f71e6038 R14: 00007fa2f71e5fa0 R15: 00007ffee539e9b8
 </TASK>
------------[ cut here ]------------
WARNING: CPU: 1 PID: 6466 at kernel/rcu/tree_plugin.h:443 __rcu_read_unlock+0x7a/0xe0 kernel/rcu/tree_plugin.h:443


Tested on:

commit:         1c64efcb Merge tag 'rust-rustfmt' of git://git.kernel...
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=144e83e2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9ad7b090a18654a7
dashboard link: https://syzkaller.appspot.com/bug?extid=b0cff308140f79a9c4cb
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=177bbc58580000