One thing I just noticed: If I don't register a handler for SIGUSR1 and
send one to the application while it is in TASK_KILLABLE then the
signal gets delivered.
Not really delivered... OK, it can be delivered (dequeued) before
the task sees SIGKILL, but this can be changed.
In short: in this case the task is correctly SIGKILL'ed. See sig_fatal()
in complete_signal().
If I register a signal handler for it than it
gets blocked and delivered once I resume the task.
Sure, if you have a handler, the signal is not fatal.
Shouldn't it get blocked even if I don't register a handler for it?
No.
ach, those signals make everything complicated. I though signals are
blocked until the single step is done
Yes, see uprobe_deny_signal().
but my test just showed my
something different.
I guess you missed the UTASK_SSTEP_TRAPPED logic.
But this doesn't matter. Surely we must not "block" signals _after_
the single step is done, and this is the problem.
Okay, what now?
IMHO: don't do this ;)
Blocking signals isn't probably a good idea.
This is bad and wrong idea, I think.
And, once again. Whatever you do, you can race with uprobe_register().
I mean, you must never expect that the task will hit the same uprobe
again, even if you are going to re-execute the same insn.