[PATCH][v2] rtnetlink: add rtnl_lock debug log

[Andy Shevchenko]

On Sat, May 8, 2021 at 12:11 PM Rocco Yue <rocco.yue at mediatek.com> wrote:
>
> We often encounter system hangs caused by certain process
> 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 this lightweight rtnl_lock debugging mechanism, 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 out to help locate the problem.
>
> i.e: from the following logs, we can clearly know that the pid=2206
> RfxSender_4 process holds rtnl_lock for a long time, causing the
> system to hang. And we can also speculate that the delay operation
> may be performed in devinet_ioctl(), resulting in rtnl_lock was
> not released in time.
>
> <6>[   40.191481][    C6] rtnetlink: -- rtnl_print_btrace start --

You don't seem to get it. It's a quite long trace for the commit
message. Do you need all those lines below? Why?

> <6>[   40.191494][    C6] rtnetlink: RfxSender_4[2206][R] hold rtnl_lock
> more than 2 sec, start time: 38181400013
> <4>[   40.191510][    C6]  devinet_ioctl+0x1fc/0x75c
> <4>[   40.191517][    C6]  inet_ioctl+0xb8/0x1f8
> <4>[   40.191527][    C6]  sock_do_ioctl+0x70/0x2ac
> <4>[   40.191533][    C6]  sock_ioctl+0x5dc/0xa74
> <4>[   40.191541][    C6]  __arm64_sys_ioctl+0x178/0x1fc
> <4>[   40.191548][    C6]  el0_svc_common+0xc0/0x24c
> <4>[   40.191555][    C6]  el0_svc+0x28/0x88
> <4>[   40.191560][    C6]  el0_sync_handler+0x8c/0xf0
> <4>[   40.191566][    C6]  el0_sync+0x198/0x1c0
> <6>[   40.191571][    C6] Call trace:
> <6>[   40.191586][    C6]  rtnl_print_btrace+0xf0/0x124
> <6>[   40.191595][    C6]  call_timer_fn+0x5c/0x3b4
> <6>[   40.191602][    C6]  expire_timers+0xe0/0x49c
> <6>[   40.191609][    C6]  __run_timers+0x34c/0x48c
> <6>[   40.191616][    C6]  run_timer_softirq+0x28/0x58
> <6>[   40.191621][    C6]  efi_header_end+0x168/0x690
> <6>[   40.191628][    C6]  __irq_exit_rcu+0x108/0x124
> <6>[   40.191635][    C6]  __handle_domain_irq+0x130/0x1b4
> <6>[   40.191643][    C6]  gic_handle_irq.29882+0x6c/0x2d8
> <6>[   40.191648][    C6]  el1_irq+0xdc/0x1c0
> <6>[   40.191656][    C6]  __delay+0xc0/0x180
> <6>[   40.191663][    C6]  devinet_ioctl+0x21c/0x75c
> <6>[   40.191668][    C6]  inet_ioctl+0xb8/0x1f8
> <6>[   40.191675][    C6]  sock_do_ioctl+0x70/0x2ac
> <6>[   40.191682][    C6]  sock_ioctl+0x5dc/0xa74
> <6>[   40.191688][    C6]  __arm64_sys_ioctl+0x178/0x1fc
> <6>[   40.191694][    C6]  el0_svc_common+0xc0/0x24c
> <6>[   40.191699][    C6]  el0_svc+0x28/0x88
> <6>[   40.191705][    C6]  el0_sync_handler+0x8c/0xf0
> <6>[   40.191710][    C6]  el0_sync+0x198/0x1c0
> <6>[   40.191715][    C6] rtnetlink: -- rtnl_print_btrace end --
>
> <6>[   42.181879][ T2206] rtnetlink: rtnl_lock is held by [2206] from
> [38181400013] to [42181875177]

-- 
With Best Regards,
Andy Shevchenko