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

[Andy Shevchenko]

On Mon, May 10, 2021 at 03:23:41PM +0800, Rocco.Yue wrote:
> On Sun, 2021-05-09 at 12:42 +0300, Andy Shevchenko wrote:
> > On Sat, May 8, 2021 at 12:11 PM Rocco Yue <rocco.yue@xxxxxxxxxxxx> 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?
> > 
> 
> The contents shown in all the lines below are the original printed after
> adding this patch, I pasted these lines into commit message to
> illustrate this patch as a case.
> 
> It now appears that some of following are indeed unnecessary, I am going
> to condense a lot of following contents as follows.
> 
> Could you please help to take a look at it again? many thanks :-)
> 
> [   40.191481] rtnetlink: -- rtnl_print_btrace start --
> [   40.191494] RfxSender_4[2206][R] hold rtnl_lock more than 2 sec,
> start time: 38181400013
> [   40.191571] Call trace:
> [   40.191586]  rtnl_print_btrace+0xf0/0x124
> [   40.191656]  __delay+0xc0/0x180
> [   40.191663]  devinet_ioctl+0x21c/0x75c
> [   40.191668]  inet_ioctl+0xb8/0x1f8
> [   40.191675]  sock_do_ioctl+0x70/0x2ac
> [   40.191682]  sock_ioctl+0x5dc/0xa74
> [   40.191715] rtnetlink: -- rtnl_print_btrace end --
> [   42.181879] rtnetlink: rtnl_lock is held by [2206] from
> [38181400013] to [42181875177]

Much better, thanks!

(You still need a real review on the contents of the change)

> > > <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