From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f205.google.com (mail-oi1-f205.google.com [209.85.167.205]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1179123C8AE for ; Sun, 30 Aug 2026 00:30:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.205 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788049831; cv=none; b=Y+uTG6ec9uFDiPziQgzqWeVSiWdwhd7UYjWlAYyS9lcjav3NtIzEfiI/nvuE7NxvpGJGQ123mxxipdwXXtRYgPD4+4Rin82zr8bS5asO/55PqC+laDqSb6rXHQQKRup/35XtGaQn4dTOViKFaPHGgvCircX5kKWZp1P3FnS5/Wk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788049831; c=relaxed/simple; bh=HLVWaMVldZGCM1CNOfEHLO61y+UvHI0bHYIPOoaiHwg=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; 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2002:a05:6808:14c4:b0:4b3:18d2:5fa0 with SMTP id 5614622812f47-4b37ca840ddmr22776221b6e.14.1788049829067; Sat, 29 Aug 2026 17:30:29 -0700 (PDT) Date: Sat, 29 Aug 2026 17:30:29 -0700 In-Reply-To: <695e9bb5.050a0220.1c677c.0372.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6a9379a5.1d9ded08.62e62.0114.GAE@google.com> Subject: Re: [syzbot] [net?] INFO: rcu detected stall in kernfs_fop_write_iter (3) From: syzbot To: dakr@kernel.org, davem@davemloft.net, driver-core@lists.linux.dev, edumazet@google.com, gregkh@linuxfoundation.org, horms@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, pabeni@redhat.com, rafael@kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" syzbot has found a reproducer for the following issue on: HEAD commit: 1b78070aaef6 Merge tag 'net-7.3-rc1' of git://git.kernel.o.. git tree: net-next console output: https://syzkaller.appspot.com/x/log.txt?x=132ec379580000 kernel config: https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e dashboard link: https://syzkaller.appspot.com/bug?extid=10b515098afdcfc455c7 compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1208fd49580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16b92c15580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/18856a03a9a3/disk-1b78070a.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/cc2bc68d7ef4/vmlinux-1b78070a.xz kernel image: https://storage.googleapis.com/syzbot-assets/05a5e00f8f91/bzImage-1b78070a.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+10b515098afdcfc455c7@syzkaller.appspotmail.com rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 1-...!: (1 ticks this GP) idle=51bc/1/0x4000000000000000 softirq=17926/17938 fqs=6 rcu: (detected by 0, t=10502 jiffies, g=16769, q=4471 ncpus=2) Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 UID: 0 PID: 4984 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 RIP: 0010:check_preemption_disabled+0x1a/0xd0 lib/smp_processor_id.c:53 Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 55 41 57 41 56 53 65 8b 05 4b ee b0 07 65 48 8b 0d 1b ee b0 07 85 c9 74 0c 5b <41> 5e 41 5f 5d c3 cc cc cc cc cc 9c 59 f7 c1 00 02 00 00 74 ea 65 RSP: 0018:ffffc90000a18d68 EFLAGS: 00000002 RAX: 0000000000000001 RBX: 00000000ffffffff RCX: 0000000001000001 RDX: 0000000001000001 RSI: ffffffff8e48da65 RDI: ffffffff8c6d8b80 RBP: 00000000ffffffff R08: 0000000001000001 R09: 0000000000000000 R10: ffff88802b880308 R11: ffffed1005710063 R12: 0000000000000046 R13: ffff88807ed40000 R14: ffff8880b8728298 R15: ffff8880b8728390 FS: 00007f352db77880(0000) GS:ffff888124de0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055556bd98a38 CR3: 000000007efac000 CR4: 00000000003526f0 Call Trace: lockdep_recursion_inc kernel/locking/lockdep.c:465 [inline] lock_is_held_type+0x5a/0x150 kernel/locking/lockdep.c:5981 lock_is_held include/linux/lockdep.h:249 [inline] __run_hrtimer kernel/time/hrtimer.c:2033 [inline] __hrtimer_run_queues+0x20b/0xa10 kernel/time/hrtimer.c:2124 hrtimer_interrupt+0x4cd/0xaa0 kernel/time/hrtimer.c:2243 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline] __sysvec_apic_timer_interrupt+0x102/0x430 arch/x86/kernel/apic/apic.c:1068 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline] sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1062 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674 RIP: 0010:add_uevent_var+0x25f/0x460 lib/kobject_uevent.c:692 Code: 01 00 00 e8 63 ee ed f5 4c 8b 64 24 38 42 0f b6 04 3b 84 c0 48 8b 54 24 10 0f 85 aa 01 00 00 49 83 c4 18 4c 63 32 41 8d 46 01 <89> 02 bf 40 00 00 00 44 89 f6 e8 32 f3 ed f5 49 83 fe 3f 0f 87 aa RSP: 0018:ffffc9000253f880 EFLAGS: 00000286 RAX: 0000000000000009 RBX: 1ffff1100feb9043 RCX: ffff88807ed40000 RDX: ffff88807f5c8218 RSI: 000000000000007b RDI: 0000000000000801 RBP: ffffc9000253f9b0 R08: ffffc9000253f757 R09: 0000000000000000 R10: ffffc9000253f740 R11: fffff520004a7eeb R12: ffff88807f5c8018 R13: 1ffff920004a7f20 R14: 0000000000000008 R15: dffffc0000000000 dev_uevent+0x4ab/0x870 drivers/base/core.c:2774 kobject_uevent_env+0x475/0x9e0 lib/kobject_uevent.c:576 kobject_synth_uevent+0x45e/0x950 lib/kobject_uevent.c:207 uevent_store+0x26/0x70 drivers/base/core.c:2847 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f352d4a7407 Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff RSP: 002b:00007fff3d25d8b0 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f352db77880 RCX: 00007f352d4a7407 RDX: 0000000000000007 RSI: 000055716b1e2a00 RDI: 000000000000000c RBP: 000055716b1e2a00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000007 R13: 000055716b1ea8a0 R14: 00007f352d5efea0 R15: 00007fff3d25dbf0 rcu: rcu_preempt kthread starved for 10472 jiffies! g16769 f0x0 RCU_GP_WAIT_FQS(5) ->state=R ->cpu=0 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:27496 pid:17 tgid:17 ppid:2 task_flags:0x208040 flags:0x00080000 Call Trace: context_switch kernel/sched/core.c:5520 [inline] __schedule+0x17d4/0x5820 kernel/sched/core.c:7270 __schedule_loop kernel/sched/core.c:7347 [inline] schedule+0x164/0x2b0 kernel/sched/core.c:7362 schedule_timeout+0x152/0x2c0 kernel/time/sleep_timeout.c:99 rcu_gp_fqs_loop+0x30c/0x11f0 kernel/rcu/tree.c:2122 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2330 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 rcu: Stack dump where RCU GP kthread last ran: CPU: 0 UID: 0 PID: 5760 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 RIP: 0010:csd_lock_wait kernel/smp.c:363 [inline] RIP: 0010:csd_lock kernel/smp.c:396 [inline] RIP: 0010:smp_call_function_many_cond+0x61e/0x1500 kernel/smp.c:944 Code: b6 04 04 84 c0 0f 85 d5 03 00 00 44 8b 3b 44 89 fe 83 e6 01 31 ff e8 51 51 0c 00 41 83 e7 01 75 07 e8 46 4c 0c 00 eb 3f f3 90 <48> b8 00 00 00 00 00 fc ff df 41 0f b6 04 04 84 c0 75 0f f7 03 01 RSP: 0018:ffffc9000355f420 EFLAGS: 00000293 RAX: ffffffff81bb677e RBX: ffff8880b87414c8 RCX: ffff888020330000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000 RBP: ffffc9000355f570 R08: ffff88802033159f R09: 1ffff110040662b3 R10: dffffc0000000000 R11: 0000000000000000 R12: 1ffff110170e8299 R13: 0000000000000001 R14: ffff8880b87414c0 R15: 0000000000000001 FS: 000055556bd7d500(0000) GS:ffff888124ce0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fe76eb556c8 CR3: 000000007b140000 CR4: 00000000003526f0 Call Trace: __flush_tlb_multi arch/x86/include/asm/paravirt.h:46 [inline] flush_tlb_multi arch/x86/mm/tlb.c:1361 [inline] flush_tlb_mm_range+0x8ff/0x1090 arch/x86/mm/tlb.c:1435 dup_mmap+0x1758/0x1dc0 mm/mmap.c:1884 dup_mm kernel/fork.c:1543 [inline] copy_mm+0x11a/0x480 kernel/fork.c:1595 copy_process+0x1e75/0x43e0 kernel/fork.c:2307 kernel_clone+0x2d7/0x940 kernel/fork.c:2766 __do_sys_clone kernel/fork.c:2908 [inline] __se_sys_clone kernel/fork.c:2892 [inline] __x64_sys_clone+0x1b6/0x230 kernel/fork.c:2892 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fe76ddc6bd2 Code: 89 e7 e8 71 8b f7 ff 45 31 c0 31 d2 31 f6 64 48 8b 04 25 10 00 00 00 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 66 89 c5 85 c0 75 3b 64 48 8b 04 25 10 00 00 RSP: 002b:00007ffc068b1d70 EFLAGS: 00000246 ORIG_RAX: 0000000000000038 RAX: ffffffffffffffda RBX: 00007ffc068b1d70 RCX: 00007fe76ddc6bd2 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011 RBP: 00007ffc068b1efc R08: 0000000000000000 R09: 0000000000000000 R10: 000055556bd7d7d0 R11: 0000000000000246 R12: 0000000000000001 R13: 000055556bd90a00 R14: 000000000001ae67 R15: 00007ffc068b1f50 --- 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.