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Message-ID: <693aca04.050a0220.4004e.0347.GAE@google.com> Date: Thu, 11 Dec 2025 05:41:24 -0800 From: syzbot <syzbot+0f5d9b52b3f467f78d36@...kaller.appspotmail.com> To: bp@...en8.de, brauner@...nel.org, dave.hansen@...ux.intel.com, hpa@...or.com, jack@...e.cz, linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, mingo@...hat.com, netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com, tglx@...utronix.de, viro@...iv.linux.org.uk, x86@...nel.org Subject: Re: [syzbot] [ext4?] INFO: rcu detected stall in unwind_next_frame (5) syzbot has found a reproducer for the following issue on: HEAD commit: 5ce74bc1b7cb Add linux-next specific files for 20251211 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=10fd91c2580000 kernel config: https://syzkaller.appspot.com/x/.config?x=b9f785244b836412 dashboard link: https://syzkaller.appspot.com/bug?extid=0f5d9b52b3f467f78d36 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=14a2261a580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16f00592580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/e550c10060d5/disk-5ce74bc1.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/80331ba2b4cc/vmlinux-5ce74bc1.xz kernel image: https://storage.googleapis.com/syzbot-assets/4bcb4f82dfcf/bzImage-5ce74bc1.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+0f5d9b52b3f467f78d36@...kaller.appspotmail.com rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P5976/1:b..l rcu: (detected by 1, t=10502 jiffies, g=13301, q=280 ncpus=2) task:kworker/u8:2 state:R running task stack:24320 pid:5976 tgid:5976 ppid:2 task_flags:0x4208060 flags:0x00080000 Workqueue: kvfree_rcu_reclaim kfree_rcu_work Call Trace: <TASK> context_switch kernel/sched/core.c:5256 [inline] __schedule+0x14bc/0x5000 kernel/sched/core.c:6863 preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7190 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 74 e0 24 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:ffffc90003a772d8 EFLAGS: 00000206 RAX: a754b79da94c6400 RBX: 0000000000000000 RCX: a754b79da94c6400 RDX: 00000000c3648bbc RSI: ffffffff8dc8f224 RDI: ffffffff8be251e0 RBP: ffffffff81747f85 R08: ffffffff81747f85 R09: ffffffff8e341a60 R10: ffffc90003a77498 R11: ffffffff81ade980 R12: 0000000000000002 R13: ffffffff8e341a60 R14: 0000000000000000 R15: 0000000000000246 rcu_lock_acquire include/linux/rcupdate.h:331 [inline] rcu_read_lock include/linux/rcupdate.h:867 [inline] class_rcu_constructor include/linux/rcupdate.h:1195 [inline] unwind_next_frame+0xc2/0x23d0 arch/x86/kernel/unwind_orc.c:495 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_freelist_hook mm/slub.c:2569 [inline] slab_free_bulk mm/slub.c:6703 [inline] kmem_cache_free_bulk+0x3fb/0xdb0 mm/slub.c:7390 kfree_bulk include/linux/slab.h:830 [inline] kvfree_rcu_bulk+0xe5/0x1f0 mm/slab_common.c:1523 kfree_rcu_work+0xed/0x170 mm/slab_common.c:1601 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 10543 jiffies! g13301 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:27136 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00080000 Call Trace: <TASK> context_switch kernel/sched/core.c:5256 [inline] __schedule+0x14bc/0x5000 kernel/sched/core.c:6863 __schedule_loop kernel/sched/core.c:6945 [inline] schedule+0x165/0x360 kernel/sched/core.c:6960 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 13 d0 22 00 f3 0f 1e fa fb f4 <e9> c8 ed 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: 77582282823a1b00 RBX: ffffffff8197d83a RCX: 77582282823a1b00 RDX: 0000000000000001 RSI: ffffffff8daa54ce RDI: ffffffff8be251e0 RBP: ffffc90000197f10 R08: ffff8880b87336db R09: 1ffff110170e66db R10: dffffc0000000000 R11: ffffed10170e66dc R12: ffffffff8fc3cc70 R13: 1ffff11003adcb70 R14: 0000000000000001 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff888125ae6000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000002200 CR3: 0000000075c16000 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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