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Subject: Re: [syzbot] INFO: rcu detected stall in
 prog_array_map_clear_deferred
To:     syzbot <syzbot+1e372cc42ba6b9d90a6b@syzkaller.appspotmail.com>,
        andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, john.fastabend@gmail.com, kafai@fb.com,
        kpsingh@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, songliubraving@fb.com,
        syzkaller-bugs@googlegroups.com, yhs@fb.com
References: <000000000000a8f39905ceacaf6b@google.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <96b76ce6-40bd-0a25-e9af-a0626f5a8b82@gmail.com>
Date:   Mon, 18 Oct 2021 21:07:28 -0700
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On 10/18/21 8:59 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    7c832d2f9b95 Add linux-next specific files for 20211015
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13d749ccb00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f6ac42766a768877
> dashboard link: https://syzkaller.appspot.com/bug?extid=1e372cc42ba6b9d90a6b
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1702b644b00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16f91334b00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+1e372cc42ba6b9d90a6b@syzkaller.appspotmail.com
> 
> rcu: INFO: rcu_preempt self-detected stall on CPU
> rcu: 	1-...!: (1 GPs behind) idle=38d/1/0x4000000000000000 softirq=10159/10160 fqs=234 
> 	(t=10500 jiffies g=11181 q=11)
> rcu: rcu_preempt kthread starved for 9849 jiffies! g11181 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:29304 pid:   14 ppid:     2 flags:0x00004000
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:4965 [inline]
>  __schedule+0xa9a/0x4940 kernel/sched/core.c:6246
>  schedule+0xd2/0x260 kernel/sched/core.c:6319
>  schedule_timeout+0x14a/0x2a0 kernel/time/timer.c:1881
>  rcu_gp_fqs_loop+0x186/0x810 kernel/rcu/tree.c:1966
>  rcu_gp_kthread+0x1de/0x320 kernel/rcu/tree.c:2139
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>  </TASK>
> rcu: Stack dump where RCU GP kthread last ran:
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 PID: 2713 Comm: kworker/0:3 Not tainted 5.15.0-rc5-next-20211015-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events prog_array_map_clear_deferred
> RIP: 0010:check_preemption_disabled+0x2/0x170 lib/smp_processor_id.c:13
> Code: 1f 44 00 00 e8 6f 16 4e f8 65 48 8b 3c 25 40 70 02 00 e8 41 43 05 f8 eb 99 0f 1f 44 00 00 0f 0b e9 23 ff ff ff cc cc cc 41 56 <41> 55 49 89 f5 41 54 55 48 89 fd 53 0f 1f 44 00 00 65 44 8b 25 cd
> RSP: 0018:ffffc9000b95fa68 EFLAGS: 00000046
> RAX: 0000000000000002 RBX: c8757c4f6cfa24cc RCX: ffffc9000b95fac8
> RDX: 1ffff110046b014b RSI: ffffffff89ac08c0 RDI: ffffffff8a046f60
> RBP: 1ffff9200172bf51 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000002
> R13: 0000000000000003 R14: ffff888023580a60 R15: ffff888023580000
> FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005555567352c0 CR3: 000000000b88e000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  lockdep_recursion_finish kernel/locking/lockdep.c:438 [inline]
>  lock_release+0x3bb/0x720 kernel/locking/lockdep.c:5659
>  __mutex_unlock_slowpath+0x99/0x5e0 kernel/locking/mutex.c:892
>  fd_array_map_delete_elem+0x1b0/0x2e0 kernel/bpf/arraymap.c:824
>  bpf_fd_array_map_clear kernel/bpf/arraymap.c:871 [inline]
>  prog_array_map_clear_deferred+0x10b/0x1b0 kernel/bpf/arraymap.c:1050
>  process_one_work+0x9b2/0x1690 kernel/workqueue.c:2297
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>  </TASK>
> NMI backtrace for cpu 1
> CPU: 1 PID: 23 Comm: kworker/1:1 Not tainted 5.15.0-rc5-next-20211015-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events prog_array_map_clear_deferred
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>  nmi_cpu_backtrace.cold+0x47/0x144 lib/nmi_backtrace.c:105
>  nmi_trigger_cpumask_backtrace+0x1ae/0x220 lib/nmi_backtrace.c:62
>  trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
>  rcu_dump_cpu_stacks+0x25e/0x3f0 kernel/rcu/tree_stall.h:343
>  print_cpu_stall kernel/rcu/tree_stall.h:604 [inline]
>  check_cpu_stall kernel/rcu/tree_stall.h:688 [inline]
>  rcu_pending kernel/rcu/tree.c:3889 [inline]
>  rcu_sched_clock_irq.cold+0x9d/0x746 kernel/rcu/tree.c:2608
>  update_process_times+0x16d/0x200 kernel/time/timer.c:1785
>  tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226
>  tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1428
>  __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
>  __hrtimer_run_queues+0x1c0/0xe50 kernel/time/hrtimer.c:1749
>  hrtimer_interrupt+0x31c/0x790 kernel/time/hrtimer.c:1811
>  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]
>  __sysvec_apic_timer_interrupt+0x146/0x530 arch/x86/kernel/apic/apic.c:1103
>  sysvec_apic_timer_interrupt+0x8e/0xc0 arch/x86/kernel/apic/apic.c:1097
>  </IRQ>
>  <TASK>
>  asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
> RIP: 0010:lock_is_held_type+0xff/0x140 kernel/locking/lockdep.c:5685
> Code: 00 00 b8 ff ff ff ff 65 0f c1 05 0c 1a b5 76 83 f8 01 75 29 9c 58 f6 c4 02 75 3d 48 f7 04 24 00 02 00 00 74 01 fb 48 83 c4 08 <44> 89 e8 5b 5d 41 5c 41 5d 41 5e 41 5f c3 45 31 ed eb b9 0f 0b 48
> RSP: 0018:ffffc90000ddfa30 EFLAGS: 00000296
> RAX: 0000000000000046 RBX: 0000000000000003 RCX: 0000000000000001
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: ffffffff8bb82de0 R08: 0000000000000000 R09: ffffffff8d8fd297
> R10: fffffbfff1b1fa52 R11: 0000000000000000 R12: ffff8880157b0000
> R13: 0000000000000000 R14: 00000000ffffffff R15: ffff8880157b0ab8
>  lock_is_held include/linux/lockdep.h:283 [inline]
>  rcu_read_lock_sched_held+0x3a/0x70 kernel/rcu/update.c:125
>  trace_lock_release include/trace/events/lock.h:58 [inline]
>  lock_release+0x522/0x720 kernel/locking/lockdep.c:5648
>  __mutex_unlock_slowpath+0x99/0x5e0 kernel/locking/mutex.c:892
>  fd_array_map_delete_elem+0x1b0/0x2e0 kernel/bpf/arraymap.c:824
>  bpf_fd_array_map_clear kernel/bpf/arraymap.c:871 [inline]
>  prog_array_map_clear_deferred+0x10b/0x1b0 kernel/bpf/arraymap.c:1050
>  process_one_work+0x9b2/0x1690 kernel/workqueue.c:2297
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>  </TASK>
> ----------------
> Code disassembly (best guess), 1 bytes skipped:
>    0:	44 00 00             	add    %r8b,(%rax)
>    3:	e8 6f 16 4e f8       	callq  0xf84e1677
>    8:	65 48 8b 3c 25 40 70 	mov    %gs:0x27040,%rdi
>    f:	02 00
>   11:	e8 41 43 05 f8       	callq  0xf8054357
>   16:	eb 99                	jmp    0xffffffb1
>   18:	0f 1f 44 00 00       	nopl   0x0(%rax,%rax,1)
>   1d:	0f 0b                	ud2
>   1f:	e9 23 ff ff ff       	jmpq   0xffffff47
>   24:	cc                   	int3
>   25:	cc                   	int3
>   26:	cc                   	int3
>   27:	41 56                	push   %r14
> * 29:	41 55                	push   %r13 <-- trapping instruction
>   2b:	49 89 f5             	mov    %rsi,%r13
>   2e:	41 54                	push   %r12
>   30:	55                   	push   %rbp
>   31:	48 89 fd             	mov    %rdi,%rbp
>   34:	53                   	push   %rbx
>   35:	0f 1f 44 00 00       	nopl   0x0(%rax,%rax,1)
>   3a:	65                   	gs
>   3b:	44                   	rex.R
>   3c:	8b                   	.byte 0x8b
>   3d:	25                   	.byte 0x25
>   3e:	cd                   	.byte 0xcd
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

Repro allocates quite a big array.

bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PROG_ARRAY, key_size=4, value_size=4, max_entries=268435458, map_flags=0, inner_map_fd=-1, map_name="", map_ifindex=0, btf_fd=-1, btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0}, 64)

An ad-hoc cond_resched() would avoid this splat.