Regarding Dtrace on Arm

[Mark Johnston]

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