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Message-ID: <f48b92b5-2f77-1acd-1916-0d3ac266b632@huawei.com>
Date:   Wed, 19 Oct 2022 11:03:56 +0800
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Subject: Re: [BUG] possible deadlock in __rcu_irq_enter_check_tick
Content-Language: en-US
To:     Mark Rutland <mark.rutland@arm.com>,
        "Paul E. McKenney" <paulmck@kernel.org>
CC:     "liwei (GF)" <liwei391@huawei.com>, <linux-kernel@vger.kernel.org>,
        <rcu@vger.kernel.org>
References: <e015e32d-d068-2d17-1ca5-c584c30ffebb@huawei.com>
 <20221012064911.GN4221@paulmck-ThinkPad-P17-Gen-1> <Y063MGk3oVg6ney0@lakrids>
From:   Yu Liao <liaoyu15@huawei.com>
In-Reply-To: <Y063MGk3oVg6ney0@lakrids>
Content-Type: text/plain; charset="UTF-8"
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On 2022/10/18 22:24, 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.
> 
> Thanks,
> Mark.
> 
Correct! I made the following small modification (just for easy reproduction)
and probe the update_rq_clock() called by ttwu_queue() in the rq->lock
critical section, this issue reproduced quickly on kernel-v5.10.135.

@@ -942,7 +942,7 @@ void __rcu_irq_enter_check_tick(void)
                         "Illegal rcu_irq_enter_check_tick() from extended
quiescent state");

        if (!tick_nohz_full_cpu(rdp->cpu) ||
-           !READ_ONCE(rdp->rcu_urgent_qs) ||
+           //!READ_ONCE(rdp->rcu_urgent_qs) ||
            READ_ONCE(rdp->rcu_forced_tick)) {
                // RCU doesn't need nohz_full help from this CPU, or it is
                // already getting that help.

And I tried Zhang Qiang's modification, it can address this issue.
>>> [ 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);
>>>     }
>>> }
>>>
>