Help regarding RT kernel on ARM v7

[Vignesh Radhakrishnan]

This seems to have hit RCU stalls here which got solved while detecting
this. This happens when a grace period is not completed for more than 21
seconds (modifiable timeout from config).

If you are able to reproduce this, can you try the following things :

1.  Enable lockdep and use debug_show_all_locks() API inside the stall
detection code to see who are holding the read locks and figure out why
they are not releasing it
2.  Enable RCU_DEBUGGING options from config and get data points from those
to see what is happening using ftrace.

Thanks and regards,
Vignesh Radhakrishnan

On Wed, Jan 14, 2015 at 9:00 AM, meenakshi aggarwal <meenu23688 at gmail.com>
wrote:

> Hi,
>
>
>
>
> I am receiving following kernel warning while running kernel
>
> “3.12.19-rt30+ #6 SMP PREEMPT RT Tue Jan 13 15:35:39 IST 2015 armv7l
> GNU/Linux” on ARM v7 platform.
>
>
>
> Kindly help.
>
>
>
>
>
> [ 1044.465822] libphy: mdio at 2d24000:02 - Link is Up - 1000/Full
>
> [ 1058.805821] libphy: mdio at 2d24000:00 - Link is Up - 1000/Full
>
> [ 1662.764689] ------------[ cut here ]------------
>
> [ 1662.768867] WARNING: CPU: 1 PID: 18 at net/sched/sch_generic.c:279
> dev_watchdog+0x137/0x198()
>
> [ 1662.777581] NETDEV WATCHDOG: eth1 (fsl-gianfar): transmit queue 0 timed
> out
>
> [ 1662.876129] Modules linked in:
>
> [ 1662.885557] CPU: 1 PID: 18 Comm: ksoftirqd/1 Not tainted 3.12.19-rt30+
> #1
>
> [ 1662.885609] [<80010991>] (unwind_backtrace+0x1/0x88) from [<8000e677>]
> (show_stack+0xb/0xc)
>
> [ 1662.885628] [<8000e677>] (show_stack+0xb/0xc) from [<803024d3>]
> (dump_stack+0x4b/0x84)
>
> [ 1662.885646] [<803024d3>] (dump_stack+0x4b/0x84) from [<80018d4d>]
> (warn_slowpath_common+0x45/0x64)
>
> [ 1662.885660] [<80018d4d>] (warn_slowpath_common+0x45/0x64) from
> [<80018d87>] (warn_slowpath_fmt+0x1b/0x24)
>
> [ 1662.885678] [<80018d87>] (warn_slowpath_fmt+0x1b/0x24) from
> [<8029e5b7>] (dev_watchdog+0x137/0x198)
>
> [ 1662.885697] [<8029e5b7>] (dev_watchdog+0x137/0x198) from [<8001fe53>]
> (call_timer_fn.isra.32+0x17/0x54)
>
> [ 1662.885712] [<8001fe53>] (call_timer_fn.isra.32+0x17/0x54) from
> [<8001ff97>] (run_timer_softirq+0x107/0x140)
>
> [ 1662.885725] [<8001ff97>] (run_timer_softirq+0x107/0x140) from
> [<8001b7ad>] (do_current_softirqs+0x105/0x1cc)
>
> [ 1662.885737] [<8001b7ad>] (do_current_softirqs+0x105/0x1cc) from
> [<8001b9cb>] (run_ksoftirqd+0x23/0x38)
>
> [ 1662.885754] [<8001b9cb>] (run_ksoftirqd+0x23/0x38) from [<8002fb15>]
> (smpboot_thread_fn+0x175/0x188)
>
> [ 1662.885769] [<8002fb15>] (smpboot_thread_fn+0x175/0x188) from
> [<8002a945>] (kthread+0x5d/0x6c)
>
> [ 1662.885784] [<8002a945>] (kthread+0x5d/0x6c) from [<8000c339>]
> (ret_from_fork+0x11/0x38)
>
> [ 1662.893114] ---[ end trace 0000000000000002 ]---
>
> [ 1682.685516] INFO: rcu_preempt detected stalls on CPUs/tasks: {}
> (detected by 1, t=2102 jiffies, g=489, c=488, q=1155)
>
> [ 1682.685520] INFO: Stall ended before state dump start
>
>
>
>
> Thanks & Regards
> Meenakshi Aggarwal
>
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>
>


-- 
http://vigneshradhakrishnan.blogspot.com/
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