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Date: Tue, 18 Oct 2022 15:24:48 +0100
From: Mark Rutland <mark.rutland@....com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Yu Liao <liaoyu15@...wei.com>, "liwei (GF)" <liwei391@...wei.com>,
linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: [BUG] possible deadlock in __rcu_irq_enter_check_tick
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.
> > [ 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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