lkml.org 
[lkml]   [2021]   [Apr]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] rtnetlink: add rtnl_lock debug log
On Thu, Apr 29, 2021 at 10:21 AM Rocco Yue <rocco.yue@mediatek.com> wrote:
>
> We often encounter system hangs caused by certain processes
> holding rtnl_lock for a long time. Even if there is a lock
> detection mechanism in Linux, it is a bit troublesome and
> affects the system performance. We hope to add a lightweight
> debugging mechanism for detecting rtnl_lock.
>
> Up to now, we have discovered and solved some potential bugs
> through such debug information of this lightweight rtnl_lock,
> which is helpful for us.
>
> When you say Y for RTNL_LOCK_DEBUG, then the kernel will detect
> if any function hold rtnl_lock too long and some key information
> will be printed to help identify the issue point.
>
> i.e: from the following logs, we can clear know that the pid=5546

clearly

> RfxSender_4 process hold rtnl_lock for a long time, causing the

holds

> system hang. And we can also speculate that the delay operation

to hang

> may be performed in devinet_ioctl(), resulting in rtnl_lock was
> not released in time.
>
> <6>[ 141.151364] ----------- rtnl_print_btrace start -----------

Can you, please, shrink this to the point?

> <6>[ 141.152079] RfxSender_4[5546][R] hold rtnl_lock more than 2 sec,
> start time: 139129481562
> <4>[ 141.153114] rtnl_lock+0x88/0xfc
> <4>[ 141.153523] devinet_ioctl+0x190/0x1268
> <4>[ 141.154007] inet_ioctl+0x108/0x1f4
> <4>[ 141.154449] sock_do_ioctl+0x88/0x200
> <4>[ 141.154911] sock_ioctl+0x4b0/0x884
> <4>[ 141.155367] do_vfs_ioctl+0x6b0/0xcc4
> <4>[ 141.155830] __arm64_sys_ioctl+0xc0/0xec
> <4>[ 141.156326] el0_svc_common+0x130/0x2c0
> <4>[ 141.156810] el0_svc_handler+0xd0/0xe0
> <4>[ 141.157283] el0_svc+0x8/0xc
> <4>[ 141.157646] Call trace:
> <4>[ 141.157956] dump_backtrace+0x0/0x240
> <4>[ 141.158418] show_stack+0x18/0x24
> <4>[ 141.158836] rtnl_print_btrace+0x138/0x1cc
> <4>[ 141.159362] call_timer_fn+0x120/0x47c
> <4>[ 141.159834] expire_timers+0x28c/0x420
> <4>[ 141.160306] __run_timers+0x3d0/0x494
> <4>[ 141.160768] run_timer_softirq+0x24/0x48
> <4>[ 141.161262] __do_softirq+0x26c/0x968
> <4>[ 141.161725] irq_exit+0x1f8/0x2b4
> <4>[ 141.162145] __handle_domain_irq+0xdc/0x15c
> <4>[ 141.162672] gic_handle_irq+0xe4/0x188
> <4>[ 141.163144] el1_irq+0x104/0x200
> <4>[ 141.163559] __const_udelay+0x118/0x1b0
> <4>[ 141.164044] devinet_ioctl+0x1a0/0x1268
> <4>[ 141.164527] inet_ioctl+0x108/0x1f4
> <4>[ 141.164968] sock_do_ioctl+0x88/0x200
> <4>[ 141.165428] sock_ioctl+0x4b0/0x884
> <4>[ 141.165868] do_vfs_ioctl+0x6b0/0xcc4
> <4>[ 141.166330] __arm64_sys_ioctl+0xc0/0xec
> <4>[ 141.166825] el0_svc_common+0x130/0x2c0
> <4>[ 141.167308] el0_svc_handler+0xd0/0xe0
> <4>[ 141.167786] el0_svc+0x8/0xc
> <6>[ 141.168153] ------------ rtnl_print_btrace end -----------
>
> <6>[ 147.321389] rtnl_lock is held by [5546] from
> [139129481562] to [147321378812]


...

> +static struct rtnl_debug_btrace_t rtnl_instance = {
> + .task = NULL,
> + .pid = 0,
> + .start_time = 0,
> + .end_time = 0,
> + .nr_entries = 0,

static assumes all 0:s, what's the point?

> +};

...

> +static void rtnl_print_btrace(struct timer_list *unused)
> +{
> + pr_info("----------- %s start -----------\n", __func__);
> + pr_info("%s[%d][%c] hold rtnl_lock more than 2 sec, start time: %llu\n",
> + rtnl_instance.task->comm,
> + rtnl_instance.pid,
> + task_state_to_char(rtnl_instance.task),
> + rtnl_instance.start_time);
> + stack_trace_print(rtnl_instance.addrs, rtnl_instance.nr_entries, 0);

> + show_stack(rtnl_instance.task, NULL, KERN_DEBUG);

Unaligned debug level.

> + pr_info("------------ %s end -----------\n", __func__);

Looking into tons of these, perhaps you need to define pr_fmt(). I
haven't checked if it's already defined, though.

> +}

...

> + if (rtnl_instance.end_time - rtnl_instance.start_time > 2000000000ULL) {

Perhaps you should use one of the defined constants from time64.h ?

> + pr_info("rtnl_lock is held by [%d] from [%llu] to [%llu]\n",
> + rtnl_instance.pid,
> + rtnl_instance.start_time,
> + rtnl_instance.end_time);
> + }

--
With Best Regards,
Andy Shevchenko

\
 
 \ /
  Last update: 2021-04-29 11:32    [W:0.060 / U:12.548 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site