also, this is x86-32 machine with a single Celeron processor 1.5Ghz.

On Sun, Feb 5, 2012 at 11:57 AM, Raz [off-list ref] wrote:

Hey Steven

This is the first time I try frace on this kernel. it turned out that
when enabling
ftrace kernel oops whenever one loads a module - see bellow.
I debugged it a little and the null pointer is in   trace_module_add_events
in the loop , the call pointer is NULL.

for_each_event(call, start, end) {
  call is null.
}

I will continue debugging it a bit more.


   4.137324] e100 0000:02:03.0: eth0: NIC Link is Up 100 Mbps Full Duplex
[    5.180354] Disabling lock debugging due to kernel taint
[    5.180792] BUG: unable to handle kernel NULL pointer dereference at   (null)
[    5.180799] IP: [<c1084f7c>] trace_module_notify+0x9c/0x160
[    5.180810] *pde = 00000000
[    5.180813] Oops: 0000 [#1] PREEMPT
[    5.180818] Modules linked in: sercos_driver(O+)
[    5.180822]
[    5.180826] Pid: 1079, comm: modprobe Tainted: G           O
3.2.0-rc5-rt8 #8 N/A  N/A /MODB
[    5.180832] EIP: 0060:[<c1084f7c>] EFLAGS: 00010286 CPU: 0
[    5.180836] EIP is at trace_module_notify+0x9c/0x160
[    5.180839] EAX: de513f44 EBX: dfeecc60 ECX: de513e0c EDX: de513e74
[    5.180842] ESI: 00000000 EDI: de513edc EBP: de60df3c ESP: de60df14
[    5.180846]  DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
[    5.180849] Process modprobe (pid: 1079, ti=de60c000 task=de519030
task.ti=de60c000)
[    5.180852] Stack:
[    5.180854]  de513e74 de513f44 de513edc de513f44 de513e0c de513e74
7fbb1b30 c14578b0
[    5.180859]  00000000 c14563a0 de60df58 c1055ba5 dfeecc60 00000001
c1455d50 00000001
[    5.180865]  dfeecc60 de60df78 c1055ee3 fffffffd 00000000 00000000
dfeecc60 0000223f
[    5.180870] Call Trace:
[    5.180878]  [<c1055ba5>] notifier_call_chain+0x45/0x60
[    5.180883]  [<c1055ee3>] __blocking_notifier_call_chain+0x43/0x70
[    5.180888]  [<c1055f2f>] blocking_notifier_call_chain+0x1f/0x30
[    5.180893]  [<c1069682>] sys_init_module+0x62/0x1c0
[    5.180900]  [<c10c32c1>] ? sys_close+0x71/0xc0
[    5.180906]  [<c13441e1>] syscall_call+0x7/0xb
[    5.180909] Code: 00 8d 90 44 01 00 00 83 c0 74 89 55 e4 89 45 ec
8d b4 26 00 00 00 00 8b 45 e4 8b 55 ec 89 7c 24 08 8b 4d e8 89 44 24
04 89 14 24


On Thu, Feb 2, 2012 at 4:12 PM, Steven Rostedt [off-list ref] wrote:

quoted

On Thu, 2012-02-02 at 12:52 +0200, Raz wrote:

quoted

hey

I am trying to understand why a user space MT process behaves in an
unexpected manner.
I have real time process, which executes most of its threads in RT priority,
and from time to time a task ( medium priority ) is executing without
trying to stop.

There are times, that this task is hogging the entire process and no
other **higher*** rt priority
task is getting any cpu time.

Linux is **not** getting hogged. when setting the serial console (
irq/serial ) and its shell ( /bin/sh )
to a higher priority linux is responsive.

Observing the task list  through ps command i can see that this task's
threads when
to un-interruptible sleep.

Any idea why is it happening ?

Some ideas, but I need a lot more information.

quoted

kernel is 3.2.0-rc5-rt8.

Is this a x86 box?

Can you run a trace on the task that is going berserk?

Enable CONFIG_FUNCTION_TRACER in your kernel and do the following:

# mount -t debugfs nodev /sys/kernel/debug
# cd /sys/kernel/debug/tracing
# echo <pid-of-berserk-task> > set_ftrace_pid
# echo function > current_tracer
# cat trace

Thanks!

-- Steve

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