Re: [BUG] possible deadlock in __rcu_irq_enter_check_tick

From: Yu Liao
Date: Thu Oct 20 2022 - 09:32:50 EST

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In reply to: Mark Rutland: "Re: [BUG] possible deadlock in __rcu_irq_enter_check_tick"
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On 2022/10/19 22:14, Mark Rutland wrote:
> On Tue, Oct 18, 2022 at 03:24:48PM +0100, Mark Rutland wrote:
>> On Tue, Oct 11, 2022 at 11:49:11PM -0700, Paul E. McKenney wrote:
>>> On Tue, Oct 11, 2022 at 09:18:11PM +0800, Yu Liao wrote:
>>>> Hello,
>>>>
>>>> When I run syzkaller, a deadlock problem occurs. The call stack is as follows:
>>>> [ 1088.244366][ C1] ======================================================
>>>> [ 1088.244838][ C1] WARNING: possible circular locking dependency detected
>>>> [ 1088.245313][ C1] 5.10.0-04424-ga472e3c833d3 #1 Not tainted
>>>> [ 1088.245745][ C1] ------------------------------------------------------
>>>
>>> It is quite possible that an unfortunate set of commits were backported
>>> to v5.10. Could you please bisect?
>>>
>>>> [ 1088.246214][ C1] syz-executor.2/932 is trying to acquire lock:
>>>> [ 1088.246628][ C1] ffffa0001440c418 (rcu_node_0){..-.}-{2:2}, at:
>>>> __rcu_irq_enter_check_tick+0x128/0x2f4
>>>> [ 1088.247330][ C1]
>>>> [ 1088.247330][ C1] but task is already holding lock:
>>>> [ 1088.247830][ C1] ffff000224d0c298 (&rq->lock){-.-.}-{2:2}, at:
>>>> try_to_wake_up+0x6e0/0xd40
>>>> [ 1088.248424][ C1]
>>>> [ 1088.248424][ C1] which lock already depends on the new lock.
>>>> [ 1088.248424][ C1]
>>>> [ 1088.249127][ C1]
>>>> [ 1088.249127][ C1] the existing dependency chain (in reverse order) is:
>>>> [ 1088.249726][ C1]
>>>> [ 1088.249726][ C1] -> #1 (&rq->lock){-.-.}-{2:2}:
>>>> [ 1088.250239][ C1] validate_chain+0x6dc/0xb0c
>>>> [ 1088.250591][ C1] __lock_acquire+0x498/0x940
>>>> [ 1088.250942][ C1] lock_acquire+0x228/0x580
>>>> [ 1088.251346][ C1] _raw_spin_lock_irqsave+0xc0/0x15c
>>>> [ 1088.251758][ C1] resched_cpu+0x5c/0x110
>>>> [ 1088.252091][ C1] rcu_implicit_dynticks_qs+0x2b0/0x5d0
>>>> [ 1088.252501][ C1] force_qs_rnp+0x244/0x39c
>>>> [ 1088.252847][ C1] rcu_gp_fqs_loop+0x2e4/0x440
>>>> [ 1088.253219][ C1] rcu_gp_kthread+0x1a4/0x240
>>>> [ 1088.253597][ C1] kthread+0x20c/0x260
>>>> [ 1088.253963][ C1] ret_from_fork+0x10/0x18
>>>> [ 1088.254389][ C1]
>>>> [ 1088.254389][ C1] -> #0 (rcu_node_0){..-.}-{2:2}:
>>>> [ 1088.255296][ C1] check_prev_add+0xe0/0x105c
>>>> [ 1088.256000][ C1] check_prevs_add+0x1c8/0x3d4
>>>> [ 1088.256693][ C1] validate_chain+0x6dc/0xb0c
>>>> [ 1088.257372][ C1] __lock_acquire+0x498/0x940
>>>> [ 1088.257731][ C1] lock_acquire+0x228/0x580
>>>> [ 1088.258079][ C1] _raw_spin_lock+0xa0/0x120
>>>> [ 1088.258425][ C1] __rcu_irq_enter_check_tick+0x128/0x2f4
>>>> [ 1088.258844][ C1] rcu_nmi_enter+0xc4/0xd0
>>>
>>> This is looking like we took an interrupt while holding an rq lock.
>>> Am I reading this correctly? If so, that is bad in and of itself.
>>
>> In this case it's not an interrupt; per the entry bits below:
>>
>>>> [ 1088.259183][ C1] arm64_enter_el1_dbg+0xb0/0x160
>>>> [ 1088.259623][ C1] el1_dbg+0x28/0x50
>>>> [ 1088.260011][ C1] el1_sync_handler+0xf4/0x150
>>>> [ 1088.260481][ C1] el1_sync+0x74/0x100
>>
>> ... this is a synchronous debug exception, which is one of:
>>
>> * A hardware single-step exception
>> * A hardware watchpoint
>> * A hardware breakpoint
>> * A software breakpoint (i.e. a BRK instruction)
>>
>> ... and we have to treat those as NMIs.
>>
>> That could be a kprobe, or a WARN, etc.
>
> Having a go with v6.1-rc1, placing a kprobe on __rcu_irq_enter_check_tick()
> causes a recursive exception which triggers the stack overflow detection, so
> there are bigger problems here, and we'll need to do some further rework of the
> arm64 entry code. FWIW, x86-64 seems fine.
>
> I have a vague recollection that that there was something (some part kprobes,
> perhaps) that didn't like being called in NMI context, which is why debug
> exceptions aren't accounted as true NMIs (but get most of the same treatment).
>
> I'll have to dig into this a bit more; there are a bunch of subtle interactions
> in this area, and I don't want to put a band-aid over this without fully
> understanding the implications.
>
> Once we've figured that out for mainline, we can figure out what needs to go to
> stable.
>
> Yu, were you particularly interested in tracing __rcu_irq_enter_check_tick(),
> or did you stumble upon this by other means?
Oh，This was found with the help of the kernel fuzzer syzkaller.

Thanks,
Yu

>
> Thanks,
> Mark.
>
>>
>> Thanks,
>> Mark.
>>
>>>> [ 1088.260800][ C1] update_irq_load_avg+0x5d8/0xaa0
>>>> [ 1088.261194][ C1] update_rq_clock_task+0xb8/0x2d0
>>>> [ 1088.261595][ C1] update_rq_clock+0x8c/0x120
>>>> [ 1088.261952][ C1] try_to_wake_up+0x70c/0xd40
>>>> [ 1088.262305][ C1] wake_up_process+0x1c/0x24
>>>> [ 1088.262652][ C1] wakeup_softirqd+0x58/0x64
>>>> [ 1088.263000][ C1] __do_softirq+0x6b8/0x95c
>>>> [ 1088.263345][ C1] irq_exit+0x27c/0x2d0
>>>> [ 1088.263674][ C1] __handle_domain_irq+0x100/0x184
>>>> [ 1088.264049][ C1] gic_handle_irq+0xc0/0x760
>>>> [ 1088.264394][ C1] el1_irq+0xb8/0x140
>>>> [ 1088.264709][ C1] _raw_spin_unlock_irqrestore+0x7c/0x130
>>>> [ 1088.265134][ C1] __aarch64_insn_write+0xc4/0x100
>>>> [ 1088.265516][ C1] aarch64_insn_patch_text_nosync+0x40/0xa0
>>>> [ 1088.265942][ C1] ftrace_make_nop+0x120/0x1a4
>>>> [ 1088.266300][ C1] __ftrace_replace_code+0xdc/0x160
>>>> [ 1088.266684][ C1] ftrace_replace_code+0x100/0x1a4
>>>> [ 1088.267063][ C1] ftrace_modify_all_code+0x1a8/0x260
>>>> [ 1088.267456][ C1] arch_ftrace_update_code+0x1c/0x2c
>>>> [ 1088.267847][ C1] ftrace_run_update_code+0x38/0xa4
>>>> [ 1088.268259][ C1] ftrace_shutdown.part.0+0x2dc/0x550
>>>> [ 1088.268682][ C1] unregister_ftrace_function+0x74/0xc0
>>>> [ 1088.269117][ C1] perf_ftrace_event_register+0x130/0x1a0
>>>> [ 1088.269559][ C1] perf_trace_destroy+0x68/0x9c
>>>> [ 1088.269938][ C1] tp_perf_event_destroy+0x1c/0x2c
>>>> [ 1088.270340][ C1] _free_event+0x2f4/0x670
>>>> [ 1088.270696][ C1] put_event+0x7c/0x90
>>>> [ 1088.271031][ C1] perf_event_release_kernel+0x3c0/0x450
>>>> [ 1088.271467][ C1] perf_release+0x24/0x34
>>>> [ 1088.271824][ C1] __fput+0x1dc/0x500
>>>> [ 1088.272155][ C1] ____fput+0x24/0x30
>>>> [ 1088.272471][ C1] task_work_run+0xf4/0x1ec
>>>> [ 1088.272811][ C1] do_notify_resume+0x378/0x410
>>>> [ 1088.273180][ C1] work_pending+0xc/0x198
>>>> [ 1088.273504][ C1]
>>>> [ 1088.273504][ C1] other info that might help us debug this:
>>>> [ 1088.273504][ C1]
>>>> [ 1088.274168][ C1] Possible unsafe locking scenario:
>>>> [ 1088.274168][ C1]
>>>> [ 1088.274658][ C1] CPU0 CPU1
>>>> [ 1088.275012][ C1] ---- ----
>>>> [ 1088.275367][ C1] lock(&rq->lock);
>>>> [ 1088.275646][ C1] lock(rcu_node_0);
>>>> [ 1088.276082][ C1] lock(&rq->lock);
>>>> [ 1088.276517][ C1] lock(rcu_node_0);
>>>> [ 1088.276797][ C1]
>>>> [ 1088.276797][ C1] *** DEADLOCK ***
>>>> [ 1088.276797][ C1]
>>>> [ 1088.277339][ C1] 4 locks held by syz-executor.2/932:
>>>> [ 1088.277696][ C1] #0: ffffa000145251e8 (event_mutex){+.+.}-{3:3}, at:
>>>> perf_trace_destroy+0x34/0x9c
>>>> [ 1088.278345][ C1] #1: ffffa000144fb5a8 (ftrace_lock){+.+.}-{3:3}, at:
>>>> unregister_ftrace_function+0x2c/0xc0
>>>> [ 1088.279034][ C1] #2: ffff0000c0e0c968 (&p->pi_lock){-.-.}-{2:2}, at:
>>>> try_to_wake_up+0xbc/0xd40
>>>> [ 1088.279672][ C1] #3: ffff000224d0c298 (&rq->lock){-.-.}-{2:2}, at:
>>>> try_to_wake_up+0x6e0/0xd40
>>>> [ 1088.280300][ C1]
>>>> [ 1088.280300][ C1] stack backtrace:
>>>> [ 1088.280706][ C1] CPU: 1 PID: 932 Comm: syz-executor.2 Not tainted
>>>> 5.10.0-04424-ga472e3c833d3 #1
>>>> [ 1088.281315][ C1] Hardware name: linux,dummy-virt (DT)
>>>> [ 1088.281679][ C1] Call trace:
>>>> [ 1088.281910][ C1] dump_backtrace+0x0/0x41c
>>>> [ 1088.282218][ C1] show_stack+0x30/0x40
>>>> [ 1088.282505][ C1] dump_stack+0x1fc/0x2c0
>>>> [ 1088.282807][ C1] print_circular_bug+0x1ec/0x284
>>>> [ 1088.283149][ C1] check_noncircular+0x1cc/0x1ec
>>>> [ 1088.283486][ C1] check_prev_add+0xe0/0x105c
>>>> [ 1088.283804][ C1] check_prevs_add+0x1c8/0x3d4
>>>> [ 1088.284126][ C1] validate_chain+0x6dc/0xb0c
>>>> [ 1088.284442][ C1] __lock_acquire+0x498/0x940
>>>> [ 1088.284764][ C1] lock_acquire+0x228/0x580
>>>> [ 1088.285072][ C1] _raw_spin_lock+0xa0/0x120
>>>> [ 1088.285392][ C1] __rcu_irq_enter_check_tick+0x128/0x2f4
>>>> [ 1088.285779][ C1] rcu_nmi_enter+0xc4/0xd0
>>>> [ 1088.286082][ C1] arm64_enter_el1_dbg+0xb0/0x160
>>>> [ 1088.286420][ C1] el1_dbg+0x28/0x50
>>>> [ 1088.286689][ C1] el1_sync_handler+0xf4/0x150
>>>> [ 1088.287010][ C1] el1_sync+0x74/0x100
>>>> [ 1088.287295][ C1] update_irq_load_avg+0x5d8/0xaa0
>>>> [ 1088.287640][ C1] update_rq_clock_task+0xb8/0x2d0
>>>> [ 1088.287988][ C1] update_rq_clock+0x8c/0x120
>>>> [ 1088.288309][ C1] try_to_wake_up+0x70c/0xd40
>>>> [ 1088.288629][ C1] wake_up_process+0x1c/0x24
>>>> [ 1088.288945][ C1] wakeup_softirqd+0x58/0x64
>>>> [ 1088.289271][ C1] __do_softirq+0x6b8/0x95c
>>>> [ 1088.289580][ C1] irq_exit+0x27c/0x2d0
>>>> [ 1088.289868][ C1] __handle_domain_irq+0x100/0x184
>>>> [ 1088.290211][ C1] gic_handle_irq+0xc0/0x760
>>>> [ 1088.290522][ C1] el1_irq+0xb8/0x140
>>>> [ 1088.290801][ C1] _raw_spin_unlock_irqrestore+0x7c/0x130
>>>> [ 1088.291188][ C1] __aarch64_insn_write+0xc4/0x100
>>>> [ 1088.291533][ C1] aarch64_insn_patch_text_nosync+0x40/0xa0
>>>> [ 1088.291928][ C1] ftrace_make_nop+0x120/0x1a4
>>>> [ 1088.292256][ C1] __ftrace_replace_code+0xdc/0x160
>>>> [ 1088.292613][ C1] ftrace_replace_code+0x100/0x1a4
>>>> [ 1088.292963][ C1] ftrace_modify_all_code+0x1a8/0x260
>>>> [ 1088.293335][ C1] arch_ftrace_update_code+0x1c/0x2c
>>>> [ 1088.293694][ C1] ftrace_run_update_code+0x38/0xa4
>>>> [ 1088.294048][ C1] ftrace_shutdown.part.0+0x2dc/0x550
>>>> [ 1088.294415][ C1] unregister_ftrace_function+0x74/0xc0
>>>> [ 1088.294787][ C1] perf_ftrace_event_register+0x130/0x1a0
>>>> [ 1088.295172][ C1] perf_trace_destroy+0x68/0x9c
>>>> [ 1088.295500][ C1] tp_perf_event_destroy+0x1c/0x2c
>>>> [ 1088.295850][ C1] _free_event+0x2f4/0x670
>>>> [ 1088.296154][ C1] put_event+0x7c/0x90
>>>> [ 1088.296439][ C1] perf_event_release_kernel+0x3c0/0x450
>>>> [ 1088.296820][ C1] perf_release+0x24/0x34
>>>> [ 1088.297125][ C1] __fput+0x1dc/0x500
>>>> [ 1088.297404][ C1] ____fput+0x24/0x30
>>>> [ 1088.297682][ C1] task_work_run+0xf4/0x1ec
>>>> [ 1088.297989][ C1] do_notify_resume+0x378/0x410
>>>> [ 1088.298316][ C1] work_pending+0xc/0x198
>>>>
>>>> I checked the code. The following scenarios may cause deadlock.
>>>>
>>>> static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
>>>> {
>>>> struct rq *rq = cpu_rq(cpu);
>>>> struct rq_flags rf;
>>>>
>>>> if (ttwu_queue_wakelist(p, cpu, wake_flags))
>>>> return;
>>>>
>>>> rq_lock(rq, &rf);
>>>> update_rq_clock(rq);
>>>> ===> el1_dbg
>>>> ->rcu_nmi_enter
>>>> ->__rcu_irq_enter_check_tick
>>>> ->raw_spin_lock_rcu_node(rdp->mynode);
>>>> ttwu_do_activate(rq, p, wake_flags, &rf);
>>>> rq_unlock(rq, &rf);
>>>> }
>>>>
>>>> static void rcu_gp_fqs(bool first_time)
>>>> {
>>>> struct rcu_node *rnp = rcu_get_root();
>>>>
>>>> WRITE_ONCE(rcu_state.gp_activity, jiffies);
>>>> WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
>>>> if (first_time) {
>>>> /* Collect dyntick-idle snapshots. */
>>>> force_qs_rnp(dyntick_save_progress_counter);
>>>> } else {
>>>> /* Handle dyntick-idle and offline CPUs. */
>>>> force_qs_rnp(rcu_implicit_dynticks_qs);
>>>> ===>raw_spin_lock_irqsave_rcu_node(rnp, flags);
>>>> ===>rcu_implicit_dynticks_qs
>>>> ->resched_cpu
>>>> ->raw_spin_lock_irqsave(&rq->lock, flags);
>>>> }
>>>> /* Clear flag to prevent immediate re-entry. */
>>>> if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
>>>> raw_spin_lock_irq_rcu_node(rnp);
>>>> WRITE_ONCE(rcu_state.gp_flags,
>>>> READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
>>>> raw_spin_unlock_irq_rcu_node(rnp);
>>>> }
>>>> }
>>>>
>

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