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Subject: Re: [RFC PATCH] rtc: add a schedule point in 'rtc_timer_do_work'
To:     Xiongfeng Wang <wangxiongfeng2@huawei.com>, <a.zummo@towertech.it>,
        <alexandre.belloni@bootlin.com>
CC:     <linux-rtc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <puranjay12@gmail.com>, <arnd@arndb.de>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        wangkefeng wang <wangkefeng.wang@huawei.com>
References: <1564054230-32742-1-git-send-email-wangxiongfeng2@huawei.com>
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
Message-ID: <6232158b-fed4-4e6a-84af-1aa6deb65608@huawei.com>
Date:   Tue, 6 Aug 2019 14:07:54 +0800
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Kindly ping...

On 2019/7/25 19:30, Xiongfeng Wang wrote:
> When I ran the syzkaller testsuite, it prints out the following calltrace.
> 
> [  138.350029] rcu: INFO: rcu_sched self-detected stall on CPU
> [  138.354703] rcu: 	2-....: (104998 ticks this GP) idle=ece/1/0x4000000000000002 softirq=2825/2825 fqs=26250
> [  138.357771] 	(t=105005 jiffies g=8033 q=1)
> [  138.358952] NMI backtrace for cpu 2
> [  138.359954] CPU: 2 PID: 170 Comm: kworker/2:1 Not tainted 5.2.0-514.55.6.9.x86_64 #64
> [  138.362212] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
> [  138.365818] Workqueue: events rtc_timer_do_work
> [  138.367122] Call Trace:
> [  138.367815]  <IRQ>
> [  138.368420]  dump_stack+0xa7/0xf9
> [  138.369372]  nmi_cpu_backtrace+0xc2/0xd0
> [  138.370516]  ? lapic_can_unplug_cpu+0xa0/0xa0
> [  138.371747]  nmi_trigger_cpumask_backtrace+0x14e/0x190
> [  138.373201]  rcu_dump_cpu_stacks+0x97/0xc5
> [  138.374376]  rcu_sched_clock_irq+0x819/0x8d0
> [  138.375571]  ? tick_sched_do_timer+0xb0/0xb0
> [  138.376787]  ? tick_sched_do_timer+0xb0/0xb0
> [  138.377991]  update_process_times+0x2d/0x60
> [  138.379176]  tick_sched_handle+0x2f/0x70
> [  138.381088]  tick_sched_timer+0x41/0x90
> [  138.382170]  __hrtimer_run_queues+0x11b/0x580
> [  138.383386]  hrtimer_interrupt+0x11b/0x280
> [  138.384585]  smp_apic_timer_interrupt+0x7a/0x230
> [  138.385909]  apic_timer_interrupt+0xf/0x20
> [  138.387066]  </IRQ>
> [  138.387668] RIP: 0010:debug_lockdep_rcu_enabled+0x6/0x30
> [  138.389149] Code: 1f 44 00 00 0f 1f 44 00 00 f0 ff 05 94 08 32 01 c3 0f 1f 00 0f 1f 44 00 00 f0 ff 0d 84 08 32 01 c3 0f 1f 00 8b 0d 2e 59 54 01 <31> c0 85 c9 74 21 8b 15 c2 b8 54 01 85 d2 74 17 65 48 8b 04 25 c0
> [  138.394395] RSP: 0018:ffffc9000080fd30 EFLAGS: 00000203 ORIG_RAX: ffffffffffffff13
> [  138.397117] RAX: 0000000000000000 RBX: ffff88813b77de10 RCX: 0000000000000002
> [  138.399104] RDX: 0000000000000000 RSI: ffffffff81886439 RDI: ffff88813b77de10
> [  138.401128] RBP: ffffc9000080fe38 R08: 0000000000000000 R09: 0000000000000000
> [  138.403149] R10: 0000000000000001 R11: 0000000000000013 R12: ffff88813b77de98
> [  138.405147] R13: ffff88813bab0c00 R14: 1a15e2eb5cd98000 R15: 000000003b9aca00
> [  138.407118]  ? rtc_timer_do_work+0x349/0x710
> [  138.408344]  rtc_timer_do_work+0x35c/0x710
> [  138.409516]  ? graph_unlock+0x41/0x80
> [  138.410591]  ? process_one_work+0x1d4/0x710
> [  138.412062]  process_one_work+0x272/0x710
> [  138.413193]  ? process_one_work+0x1d4/0x710
> [  138.414376]  worker_thread+0x58/0x520
> [  138.415405]  kthread+0x120/0x160
> [  138.416337]  ? process_one_work+0x710/0x710
> [  138.417486]  ? kthread_bind+0x20/0x20
> [  138.418526]  ret_from_fork+0x24/0x30
> 
> After looking into the syzkaller log, I found out it is caused by the
> following procedure. Firstly, enable the update interrupt through ioctl
> 'RTC_UIE_ON'. Secondly, set the rtc time to be a far further time
> through ioctl 'RTC_SET_TIME'. This will cause we stuck in
> 'rtc_timer_do_work()' because the expiring time of 'UIE' is far less
> than the current rtc time. This patch add a schedule point to avoid the
> RCU calltrace.
> 
> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
> ---
>  drivers/rtc/interface.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> index 72b7ddc4..0c8339d 100644
> --- a/drivers/rtc/interface.c
> +++ b/drivers/rtc/interface.c
> @@ -911,6 +911,8 @@ void rtc_timer_do_work(struct work_struct *work)
>  			timerqueue_add(&rtc->timerqueue, &timer->node);
>  			trace_rtc_timer_enqueue(timer);
>  		}
> +
> +		cond_resched();
>  	}
>  
>  	/* Set next alarm */
>