[Click] Help with kernel OOPS

[Vivek raghunathan]

Eddie and All,

It seems like there is a race in ToDevice::run_task that has to do
with run_task being scheduled after ToDevice::cleanup -> clear_device
-> dev_put. I am attaching a patch which fixes the resulting null
pointer derefence in ToDevice::run_task.

It seems that other elements (e.g. InfiniteSource)'s run_task methods
also sometimes trigger null pointer dereferences during
click-uninstall. (The Linux kernel is able to recover from some of
these; I suspect this is because CONFIG_DETECT_SOFTLOCKUP is enabled,
unlike the ToDevice panic which always crashed the kernel.) I'm not
too familiar with the Click module cleanup code - is it true that
Element's task handlers are always automatically unscheduled on
uninstall before the corresponding Element's cleanup method is called?

Vivek


--- todevice.cc.current 2006-09-20 16:32:58.000000000 -0500
+++ todevice.cc 2006-09-20 16:46:01.000000000 -0500
@@ -233,6 +233,12 @@
     int sent = 0;

     _runs++;
+
+    // prevent race condition during cleanup when clear_device sets _dev = 0
+    if(!_dev) {
+       _task.fast_reschedule();
+       return false;
+    }

#if LINUX_VERSION_CODE >= 0x020400
     local_bh_disable();


On 9/19/06, Vivek raghunathan <vivek.raghunathan at gmail.com> wrote:
> All,
>
> The bug I reported is not specific to my code, and is probably a
> ToDevice race condition that I was inadvertently triggering. Using the
> following configuration generates the same kernel oops with EIP at
> ToDevice::run_task() in interrupt context. (My Ethernet NIC is a Intel
> Pro/100 using the e100 driver.)
>
>   AddressInfo(MyEther 00:11:25:2D:7D:33, RemoteEther 00:11:25:47:EA:7B,
>             MyIP 10.1.1.2/8, RemoteIP 10.1.1.1/8, BroadcastAddr 10.255.255.255);
>
>   FromHost(fak0, MyIP, ETHER MyEther) -> q1::Queue
>   q1 -> [0]prio::PrioSched -> Print(test_tx, 100) -> ToDevice(eth0);
>   FromDevice(eth0) -> Print(test_rx, 100) -> SetPacketType(HOST) ->
> ToHost(fak0);
>
>   splsrc::InfiniteSource(
>   DATA \<aa bb cc dd ee ff>, LIMIT -1, STOP true);
>   splsrc -> ipenc::IPEncap(222, MyIP, BroadcastAddr);
>   ipenc -> ethenc::EtherEncap(0x0800, ff:ff:ff:ff:ff:ff, MyEther);
>   ethenc -> q2::Queue;
>   q2 -> [1]prio;
>
> -Vivek
>
>
>
> On 9/19/06, Vivek raghunathan <vivek.raghunathan at gmail.com> wrote:
> > Hi all.
> >
> > I am currently implementing a Click-based opportunistic packet
> > combination engine for use on top of IEEE 802.11. I've unit tested my
> > implementation fairly extensively in user-space, and partly
> > unit-tested in kernelspace, and haven't had any issues so far. I
> > recently moved to doing integration testing, and the code seems to run
> > okay in-kernel without any problems, except that every so often (maybe
> > 6 out of 10 times), click-uninstall causes a kernel panic in interrupt
> > context on cleanup.
> >
> > The panic seems to be related to my code on the tx output path; since
> > it only appears for a few particular configurations, and only when
> > some of my elements are introducted. The configuration I am using that
> > triggers the panic is attached.  I've also manually copied the
> > oops-trace from the screen, and attached it with this email. A
> > register dump using sysrq does not produce any additional useful info,
> > so I have excluded it. It seems like the panic is triggered somewhere
> > in ToDevice::run_task. I realize that some brain-dead bug in my code
> > is probably at fault, and am currently double-checking everything I've
> > written. I am posting here mainly because I am not sure if this is a
> > ToDevice bug that I am inadvertently triggering.
> >
> > Additionally, I'm having trouble getting ksymoops to run with click.
> > Any ideas on how I go about it? (I've also tried using kexec/kdump,
> > but it seems like these are very twitchy about what kernel config is
> > used, and have issues with the one I am using).
> >
> > Vivek
> >
> >
> > --
> >
> > ---
> >
> > *************************************
> > Vivek Raghunathan,
> > PhD student,
> > University of Illinois, Urbana-Champaign
> >
> > Contact Details:
> > 1012 W. Clark St #31,
> > Urbana IL 61801
> >
> > ph: 217-766-1868 (cell)
> >     217-333-7541 (off)
> >
> >
> >
>
>
> --
>
> ---
>
> *************************************
> Vivek Raghunathan,
> PhD student,
> University of Illinois, Urbana-Champaign
>
> Contact Details:
> 1012 W. Clark St #31,
> Urbana IL 61801
>
> ph: 217-766-1868 (cell)
>     217-333-7541 (off)
>


-- 

---

*************************************
Vivek Raghunathan,
PhD student,
University of Illinois, Urbana-Champaign

Contact Details:
1012 W. Clark St #31,
Urbana IL 61801

ph: 217-766-1868 (cell)
    217-333-7541 (off)