Re: truss -f timeout 2 sleep 10 causes breakage

On Wed, Mar 27, 2024 at 01:00:07PM +0100, Mateusz Guzik wrote:
> Top of main, but I reproduced it on stable/14-e64d827d3 as well.
> 
> Mere "timeout 2 sleep 10" correctly times out.
> 
> Running "truss -f timeout 2 sleep 10" prevents timeout from killing
> sleep and the entire thing refuses to exit, truss has to be killed off
> with SIGKILL.
The issue is because debugger can stop the debuggee, which makes the
single threading never succeed.  Supposed fix is in
	https://reviews.freebsd.org/D44523
the cost is that in principle, the debuggee now can try to break out of
the reaper kill hammer, with the help of debugger.  But this setup is
arguably too convoluted: you either control the process with reaper, or
with debugger.

> 
> Here is the best part: after doing the above, going back to mere
> "timeout 2 sleep 10" (without truss!) no longer works -- timeout gets
> stuck in the kernel: mi_switch sleepq_catch_signals sleepq_wait_sig
> _sx_xlock_hard stop_all_proc_block kern_procctl sys_procctl
> amd64_syscall fast_syscall_common
This is because the threaded workqueue thread is stuck waiting for
single-threading of the victim.

> 
> It does react to -9 though.
Not the workqueue, which is the problem.