Regarding Dtrace on Arm

[Mark Johnston]

On Wed, May 11, 2016 at 06:17:51PM +0000, Abhishek Kulkarni wrote:
> Thanks very much Mark. Should I raise a bug about this on freebsd.org?

That would be helpful, thanks.

> 
> 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