Re: LWP resume and suspend ptrace(2) API

[christos%zoulas.com@localhost (Christos Zoulas)]

On Feb 11, 12:49am, krytarowski%gmail.com@localhost (Kamil Rytarowski) wrote:
-- Subject: LWP resume and suspend ptrace(2) API

| I'm proposing an API to restore the functionality to resume or suspend a
| specified thread from execution.
| 
| This interface was implemented in the past in user-space inside
| pthread(3) with the M:N thread model (with help from removed pthread_dbg).
| 
| http://netbsd.org/~kamil/patch-00028-pt_suspend-pt_resume.txt

- The second _lwp_continue should be _lwp_suspend in the man page.
- I don't like the phrasing "Lock" and "Unlock". What are you locking here?
  Why not suspend/resume execution; or prevent/allow executiom.

| This code is close to FreeBSD and shares the same request names
| (PT_RESUME and PT_SUSPEND), however on NetBSD we pass the full pair of
| tracee's pid_t and thread's lwpid_t. FreeBSD specifies just thread ID,
| which is insufficient on NetBSD, as a single tracer can control multiple
| tracees and face duplicated lwpid_t.
| 
| I've added an interface to detect if a specific LWP has been suspended
| (or not) with extending the PT_LWPINFO interface with a new pl_event
| value PL_EVENT_SUSPENDED (next to PL_EVENT_NONE and PL_EVENT_SIGNAL).
| 
| There is a new check preventing deadlocks and ptrace(2) can set with
| this patch new errno EDEADLK. I haven't checked the existing code but it
| appears that we can deadlock tracee with current PT_CONTINUE and friends.

Otherwise nicely done :-)

christos