Thanks for the report.
On 19/03/18(Mon) 09:49, Theo Buehler wrote:
> This is a regression that came with the TOCTOU race fix in kern_sig.c 1.216:
> https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sys/kern/kern_sig.c#rev1.216
> [...]
> Now gdb just hangs there and does nothing instead of exiting as
> expected. It doesn't react to ^C but one can easily kill it with
> ^Z and then kill %%.
What happens is that the programs stays stopped. Or to be more precise
re-enter the SSTOP'd state after ptrace(PT_KILL...) has been issued by
gdb(1).
The problem comes from the fact that CURSIG() is now called twice in
userret(). That means that issignal() is also called twice. The fix
is to treat SIGKILL as special if the process is currently traced.
That's also what NetBSD is doing, so I synced our comment with their,
without a typo.
ok?
Index: kern/kern_sig.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_sig.c,v
retrieving revision 1.216
diff -u -p -r1.216 kern_sig.c
--- kern/kern_sig.c 26 Feb 2018 13:33:25 -0000 1.216
+++ kern/kern_sig.c 19 Mar 2018 11:25:34 -0000
@@ -1167,11 +1167,13 @@ issignal(struct proc *p)
(pr->ps_flags & PS_TRACED) == 0)
continue;
- if ((pr->ps_flags & (PS_TRACED | PS_PPWAIT)) == PS_TRACED) {
- /*
- * If traced, always stop, and stay
- * stopped until released by the debugger.
- */
+ /*
+ * If traced, always stop, and stay stopped until released
+ * by the debugger. If our parent process is waiting for
+ * us, don't hang as we could deadlock.
+ */
+ if (((pr->ps_flags & (PS_TRACED | PS_PPWAIT)) == PS_TRACED) &&
+ signum != SIGKILL) {
p->p_xstat = signum;
if (dolock)
