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Message-ID: <68da2403.a00a0220.102ee.0036.GAE@google.com> Date: Sun, 28 Sep 2025 23:15:31 -0700 From: syzbot <syzbot+65203730e781d98f23a0@...kaller.appspotmail.com> To: akpm@...ux-foundation.org, andrii@...nel.org, ast@...nel.org, bp@...en8.de, bpf@...r.kernel.org, daniel@...earbox.net, dave.hansen@...ux.intel.com, dvyukov@...gle.com, eddyz87@...il.com, elver@...gle.com, glider@...gle.com, haoluo@...gle.com, hpa@...or.com, john.fastabend@...il.com, jolsa@...nel.org, kasan-dev@...glegroups.com, kpsingh@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-usb@...r.kernel.org, luto@...nel.org, martin.lau@...ux.dev, mingo@...hat.com, netdev@...r.kernel.org, sdf@...ichev.me, song@...nel.org, syzkaller-bugs@...glegroups.com, tglx@...utronix.de, x86@...nel.org, yonghong.song@...ux.dev Subject: Re: [syzbot] [mm?] INFO: rcu detected stall in x64_sys_call syzbot has found a reproducer for the following issue on: HEAD commit: e835faaed2f8 net/mlx5: Expose uar access and odp page faul.. git tree: net-next console output: https://syzkaller.appspot.com/x/log.txt?x=136e2ae2580000 kernel config: https://syzkaller.appspot.com/x/.config?x=15254880b29b9ff dashboard link: https://syzkaller.appspot.com/bug?extid=65203730e781d98f23a0 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=15e58334580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1005eae2580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/6b3cd235e609/disk-e835faae.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/180c3f29b5c5/vmlinux-e835faae.xz kernel image: https://storage.googleapis.com/syzbot-assets/6b8fa2c53bdd/bzImage-e835faae.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+65203730e781d98f23a0@...kaller.appspotmail.com rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 1-...!: (1 GPs behind) idle=3cd4/1/0x4000000000000000 softirq=15457/15459 fqs=3 rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P43/2:b..l rcu: (detected by 0, t=10503 jiffies, g=9717, q=782 ncpus=2) Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 UID: 0 PID: 5901 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 RIP: 0010:hrtimer_set_expires include/linux/hrtimer.h:100 [inline] RIP: 0010:advance_sched+0x9cc/0xc90 net/sched/sch_taprio.c:988 Code: 24 18 48 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 05 e8 80 51 87 f8 4d 89 74 24 18 49 83 c4 20 4c 89 e0 <48> c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 4c 89 RSP: 0018:ffffc90000a08c70 EFLAGS: 00000086 RAX: ffff888024623360 RBX: ffff8880246232c0 RCX: dffffc0000000000 RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff888024623358 RBP: ffff88807b34d550 R08: ffff8880246232eb R09: 1ffff110048c465d R10: dffffc0000000000 R11: ffffed10048c465e R12: ffff888024623360 R13: ffff888024623000 R14: 1869abf3b67aa73f R15: ffff88807b34f400 FS: 0000000000000000(0000) GS:ffff888125d39000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055f6efacf088 CR3: 000000000df36000 CR4: 00000000003526f0 Call Trace: <IRQ> __run_hrtimer kernel/time/hrtimer.c:1761 [inline] __hrtimer_run_queues+0x529/0xc60 kernel/time/hrtimer.c:1825 hrtimer_interrupt+0x45b/0xaa0 kernel/time/hrtimer.c:1887 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1039 [inline] __sysvec_apic_timer_interrupt+0x108/0x410 arch/x86/kernel/apic/apic.c:1056 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline] sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1050 </IRQ> <TASK> asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702 RIP: 0010:deref_stack_reg+0xa/0x230 arch/x86/kernel/unwind_orc.c:402 Code: 4c 24 18 e9 f2 fe ff ff 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 55 41 57 41 56 41 55 41 54 53 <48> 83 ec 20 48 89 54 24 18 49 89 f0 49 89 ff 48 be 00 00 00 00 00 RSP: 0018:ffffc900042cf4e0 EFLAGS: 00000283 RAX: fffffffffffffff0 RBX: ffffffff9036fb70 RCX: 0000000000000000 RDX: ffffc900042cf628 RSI: ffffc900042cf720 RDI: ffffc900042cf5e8 RBP: dffffc0000000000 R08: ffffc900042cf647 R09: 0000000000000000 R10: ffffc900042cf638 R11: fffff52000859ec9 R12: ffffc900042cf720 R13: ffffc900042cf638 R14: ffffc900042cf5e8 R15: 1ffffffff206df6e unwind_next_frame+0x17c4/0x2390 arch/x86/kernel/unwind_orc.c:-1 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:47 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:388 [inline] __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405 kasan_kmalloc include/linux/kasan.h:260 [inline] __kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4407 kmalloc_noprof include/linux/slab.h:905 [inline] slab_free_hook mm/slub.c:2374 [inline] slab_free mm/slub.c:4695 [inline] kmem_cache_free+0x166/0x400 mm/slub.c:4797 exit_mmap+0x53f/0xb50 mm/mmap.c:1305 __mmput+0x118/0x430 kernel/fork.c:1129 exit_mm+0x1da/0x2c0 kernel/exit.c:582 do_exit+0x648/0x2300 kernel/exit.c:949 do_group_exit+0x21c/0x2d0 kernel/exit.c:1102 __do_sys_exit_group kernel/exit.c:1113 [inline] __se_sys_exit_group kernel/exit.c:1111 [inline] __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1111 x64_sys_call+0x21f7/0x2200 arch/x86/include/generated/asm/syscalls_64.h:232 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fd7130f16c5 Code: Unable to access opcode bytes at 0x7fd7130f169b. RSP: 002b:00007ffca03ef578 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 RAX: ffffffffffffffda RBX: 000055f6efb75130 RCX: 00007fd7130f16c5 RDX: 00000000000000e7 RSI: fffffffffffffe68 RDI: 0000000000000000 RBP: 000055f6efac3910 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffca03ef5c0 R14: 0000000000000000 R15: 0000000000000000 </TASK> INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.498 msecs task:kworker/1:1 state:R running task stack:22536 pid:43 tgid:43 ppid:2 task_flags:0x4208060 flags:0x00004000 Workqueue: mld mld_ifc_work Call Trace: <TASK> context_switch kernel/sched/core.c:5357 [inline] __schedule+0x1798/0x4cc0 kernel/sched/core.c:6961 preempt_schedule_common+0x83/0xd0 kernel/sched/core.c:7145 preempt_schedule+0xae/0xc0 kernel/sched/core.c:7169 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12 __local_bh_enable_ip+0x13e/0x1c0 kernel/softirq.c:414 local_bh_enable include/linux/bottom_half.h:33 [inline] rcu_read_unlock_bh include/linux/rcupdate.h:910 [inline] __dev_queue_xmit+0x1d79/0x3b50 net/core/dev.c:4790 neigh_output include/net/neighbour.h:547 [inline] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318 mld_sendpack+0x8d4/0xe60 net/ipv6/mcast.c:1855 mld_send_cr net/ipv6/mcast.c:2154 [inline] mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693 process_one_work kernel/workqueue.c:3236 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> rcu: rcu_preempt kthread starved for 10490 jiffies! g9717 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->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:27160 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00004000 Call Trace: <TASK> context_switch kernel/sched/core.c:5357 [inline] __schedule+0x1798/0x4cc0 kernel/sched/core.c:6961 __schedule_loop kernel/sched/core.c:7043 [inline] schedule+0x165/0x360 kernel/sched/core.c:7058 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+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> rcu: Stack dump where RCU GP kthread last ran: CPU: 0 UID: 0 PID: 1011 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Workqueue: events_unbound toggle_allocation_gate RIP: 0010:csd_lock_wait kernel/smp.c:342 [inline] RIP: 0010:smp_call_function_many_cond+0xd33/0x12d0 kernel/smp.c:877 Code: 45 8b 2c 24 44 89 ee 83 e6 01 31 ff e8 86 63 0b 00 41 83 e5 01 49 bd 00 00 00 00 00 fc ff df 75 07 e8 31 5f 0b 00 eb 38 f3 90 <42> 0f b6 04 2b 84 c0 75 11 41 f7 04 24 01 00 00 00 74 1e e8 15 5f RSP: 0018:ffffc900036a7660 EFLAGS: 00000293 RAX: ffffffff81b44fab RBX: 1ffff110170e7f69 RCX: ffff888025bada00 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000 RBP: ffffc900036a77e0 R08: ffffffff8fa30637 R09: 1ffffffff1f460c6 R10: dffffc0000000000 R11: fffffbfff1f460c7 R12: ffff8880b873fb48 R13: dffffc0000000000 R14: ffff8880b863b1c0 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff888125c39000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000300 CR3: 000000000df36000 CR4: 00000000003526f0 Call Trace: <TASK> on_each_cpu_cond_mask+0x3f/0x80 kernel/smp.c:1044 on_each_cpu include/linux/smp.h:71 [inline] smp_text_poke_sync_each_cpu arch/x86/kernel/alternative.c:2653 [inline] smp_text_poke_batch_finish+0x5f9/0x1130 arch/x86/kernel/alternative.c:2863 arch_jump_label_transform_apply+0x1c/0x30 arch/x86/kernel/jump_label.c:146 static_key_enable_cpuslocked+0x128/0x250 kernel/jump_label.c:210 static_key_enable+0x1a/0x20 kernel/jump_label.c:223 toggle_allocation_gate+0xad/0x240 mm/kfence/core.c:850 process_one_work kernel/workqueue.c:3236 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </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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