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Message-ID: <694b5ac4.050a0220.35954c.000f.GAE@google.com> Date: Tue, 23 Dec 2025 19:15:16 -0800 From: syzbot <syzbot+62348313fb96b25955aa@...kaller.appspotmail.com> To: antonio@...delbit.com, b.a.t.m.a.n@...ts.open-mesh.org, davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, kuba@...nel.org, linux-kernel@...r.kernel.org, marek.lindner@...lbox.org, netdev@...r.kernel.org, pabeni@...hat.com, sven@...fation.org, sw@...onwunderlich.de, syzkaller-bugs@...glegroups.com Subject: Re: [syzbot] [batman?] INFO: rcu detected stall in batadv_iv_send_outstanding_bat_ogm_packet (6) syzbot has found a reproducer for the following issue on: HEAD commit: cc3aa43b44bd Add linux-next specific files for 20251219 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=12b62022580000 kernel config: https://syzkaller.appspot.com/x/.config?x=da1bc82c6189c463 dashboard link: https://syzkaller.appspot.com/bug?extid=62348313fb96b25955aa compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12abdf1a580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=118eef1a580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/30bf539e6f28/disk-cc3aa43b.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/0e2f8b08e342/vmlinux-cc3aa43b.xz kernel image: https://storage.googleapis.com/syzbot-assets/ec7ee6ece11f/bzImage-cc3aa43b.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+62348313fb96b25955aa@...kaller.appspotmail.com rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P198/1:b..l P5961/1:b..l rcu: (detected by 1, t=10502 jiffies, g=13701, q=705 ncpus=2) task:udevd state:R running task stack:24376 pid:5961 tgid:5961 ppid:5200 task_flags:0x400140 flags:0x00080000 Call Trace: <TASK> context_switch kernel/sched/core.c:5258 [inline] __schedule+0x150e/0x5070 kernel/sched/core.c:6866 preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7193 irqentry_exit+0x5d8/0x660 kernel/entry/common.c:216 asm_sysvec_reschedule_ipi+0x1a/0x20 arch/x86/include/asm/idtentry.h:702 RIP: 0010:lock_release+0x2a6/0x3b0 kernel/locking/lockdep.c:5893 Code: 4d 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f7 44 24 20 00 02 00 00 75 52 f7 c3 00 02 00 00 74 01 fb 65 48 8b 05 2a 0f 01 11 <48> 3b 44 24 28 75 75 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d e9 RSP: 0018:ffffc90003aa78b0 EFLAGS: 00000206 RAX: 6d71d4c1a37b0900 RBX: 0000000000000202 RCX: 6d71d4c1a37b0900 RDX: 0000000000000000 RSI: ffffffff8db7ed49 RDI: ffffffff8be07960 RBP: ffff88802e53a9b0 R08: ffffc90003aa7b20 R09: 0000000000000000 R10: ffffc90003aa7a38 R11: fffff52000754f49 R12: 0000000000000000 R13: 0000000000000000 R14: ffffffff8e13f2e0 R15: ffff88802e539e80 rcu_lock_release include/linux/rcupdate.h:341 [inline] rcu_read_unlock include/linux/rcupdate.h:897 [inline] class_rcu_destructor include/linux/rcupdate.h:1195 [inline] unwind_next_frame+0x1ab1/0x23d0 arch/x86/kernel/unwind_orc.c:695 arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25 stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122 kasan_save_stack mm/kasan/common.c:57 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:78 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584 poison_slab_object mm/kasan/common.c:253 [inline] __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285 kasan_slab_free include/linux/kasan.h:235 [inline] slab_free_hook mm/slub.c:2540 [inline] slab_free mm/slub.c:6674 [inline] kmem_cache_free+0x197/0x620 mm/slub.c:6785 do_readlinkat+0x293/0x500 fs/stat.c:596 __do_sys_readlink fs/stat.c:613 [inline] __se_sys_readlink fs/stat.c:610 [inline] __x64_sys_readlink+0x7f/0x90 fs/stat.c:610 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fd103b153a7 RSP: 002b:00007ffefbfc23a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000059 RAX: ffffffffffffffda RBX: 00007ffefbfc2880 RCX: 00007fd103b153a7 RDX: 0000000000000400 RSI: 00007ffefbfc23b0 RDI: 00007ffefbfc2880 RBP: 00007ffefbfc23b0 R08: 000055a62739fc90 R09: 0000000000000020 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000400 R13: 00007ffefbfc30b5 R14: 000055a5fb7d0ca4 R15: 000055a5fb7d0bcc </TASK> task:kworker/u8:6 state:R running task stack:23512 pid:198 tgid:198 ppid:2 task_flags:0x4208060 flags:0x00080000 Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet Call Trace: <TASK> context_switch kernel/sched/core.c:5258 [inline] __schedule+0x150e/0x5070 kernel/sched/core.c:6866 preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7193 irqentry_exit+0x5d8/0x660 kernel/entry/common.c:216 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697 RIP: 0010:lock_acquire+0x16c/0x340 kernel/locking/lockdep.c:5872 Code: 00 00 00 00 9c 8f 44 24 30 f7 44 24 30 00 02 00 00 0f 85 cd 00 00 00 f7 44 24 08 00 02 00 00 74 01 fb 65 48 8b 05 44 41 01 11 <48> 3b 44 24 58 0f 85 e5 00 00 00 48 83 c4 60 5b 41 5c 41 5d 41 5e RSP: 0018:ffffc900030177e0 EFLAGS: 00000206 RAX: 9c7a27e9643fc600 RBX: 0000000000000000 RCX: 9c7a27e9643fc600 RDX: 00000000814aee25 RSI: ffffffff8db7ed49 RDI: ffffffff8be07960 RBP: ffffffff8b269940 R08: ffffffff8b269940 R09: ffffffff8e13f2e0 R10: dffffc0000000000 R11: ffffed100f2f1517 R12: 0000000000000002 R13: ffffffff8e13f2e0 R14: 0000000000000000 R15: 0000000000000246 rcu_lock_acquire include/linux/rcupdate.h:331 [inline] rcu_read_lock include/linux/rcupdate.h:867 [inline] batadv_iv_ogm_slide_own_bcast_window net/batman-adv/bat_iv_ogm.c:761 [inline] batadv_iv_ogm_schedule_buff net/batman-adv/bat_iv_ogm.c:833 [inline] batadv_iv_ogm_schedule+0x454/0xf00 net/batman-adv/bat_iv_ogm.c:873 batadv_iv_send_outstanding_bat_ogm_packet+0x6c6/0x7e0 net/batman-adv/bat_iv_ogm.c:1709 process_one_work+0x93a/0x15a0 kernel/workqueue.c:3279 process_scheduled_works kernel/workqueue.c:3362 [inline] worker_thread+0x9b0/0xee0 kernel/workqueue.c:3443 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 </TASK> rcu: rcu_preempt kthread starved for 10314 jiffies! g13701 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1 rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior. rcu: RCU grace-period kthread stack dump: task:rcu_preempt state:R running task stack:27232 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00080000 Call Trace: <TASK> context_switch kernel/sched/core.c:5258 [inline] __schedule+0x150e/0x5070 kernel/sched/core.c:6866 __schedule_loop kernel/sched/core.c:6948 [inline] schedule+0x165/0x360 kernel/sched/core.c:6963 schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99 rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083 rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 </TASK> rcu: Stack dump where RCU GP kthread last ran: CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82 Code: cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 9e 2a 00 f3 0f 1e fa fb f4 <e9> 48 ee 02 00 cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 RSP: 0018:ffffc90000197de0 EFLAGS: 000002c6 RAX: af5d4f71fc268f00 RBX: ffffffff819786ba RCX: af5d4f71fc268f00 RDX: 0000000000000001 RSI: ffffffff8d997e54 RDI: ffffffff8be07960 RBP: ffffc90000197f10 R08: ffff8880b87336db R09: 1ffff110170e66db R10: dffffc0000000000 R11: ffffed10170e66dc R12: ffffffff8fa22f70 R13: 1ffff11003adab70 R14: 0000000000000001 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff888125d25000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007efd7aea1f98 CR3: 0000000032c9a000 CR4: 00000000003526f0 Call Trace: <TASK> arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline] default_idle+0x13/0x20 arch/x86/kernel/process.c:767 default_idle_call+0x73/0xb0 kernel/sched/idle.c:122 cpuidle_idle_call kernel/sched/idle.c:191 [inline] do_idle+0x1ea/0x520 kernel/sched/idle.c:332 cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:430 start_secondary+0x101/0x110 arch/x86/kernel/smpboot.c:312 common_startup_64+0x13e/0x147 </TASK> --- 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.
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