Regarding Dtrace on Arm

[Abhishek Kulkarni]

Thanks very much Mark. Should I raise a bug about this on freebsd.org?

Regards
Abhishek Kulkarni




On 5/11/16, 9:49 AM, "Mark Johnston" <markjdb at gmail.com on behalf of markj at FreeBSD.org> wrote:

>On Sat, May 07, 2016 at 08:55:56PM +0000, Abhishek Kulkarni wrote:
>> Hello All,
>> 
>> I was using Dtrace  using the FBT provider on an arm platform with witness enabled. When FBT is used with the kernel module, it generates a kernel panic or the system becomes unresponsive. Is this problem know or seen before. I am copying the kernel backtrace below for reference. The issue seems to be with a blockable sleep lock(kld_sx) acquired which is conflicting with the td->td_critnest positive value.
>
>Unfortunately, I think this is expected. The ARM port of DTrace will
>call into the kernel linker from probe context to perform stack
>unwinding. This is a bug since the kernel linker cannot be entered in
>arbitrary contexts - the thread might already hold the linker lock, or
>might hold a critical section as in your example.
>
>This is a known issue, but I'm not sure if anyone is working on fixing
>it.
>
>-Mark