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SubjectRe: [patch] O(1) sys_exit(), threading, scalable-exit-2.5.31-A6
On Tue, Aug 20, 2002 at 04:36:19PM +0200, Ingo Molnar wrote:
>
> the attached patch ontop of BK-curr fixes the ptrace wait4() anomaly that
> can be observed in any previous Linux kernel i could get my hands at. So
> in fact ->ptrace_children, besides being a speedup, also fixed a bug that
> couldnt be fixed in any satisfactory way before.
>
> Ingo
>
> --- linux/kernel/exit.c.orig Tue Aug 20 16:28:57 2002
> +++ linux/kernel/exit.c Tue Aug 20 16:30:13 2002
> @@ -731,7 +731,7 @@
> tsk = next_thread(tsk);
> } while (tsk != current);
> read_unlock(&tasklist_lock);
> - if (flag) {
> + if (flag || !list_empty(&current->ptrace_children)) {
> retval = 0;
> if (options & WNOHANG)
> goto end_wait4;

Ingo,

At this point your ptrace changes have completely broken both
_TRACEME/exec and _ATTACH debugging. If an attached process finishes
while a debugger is attached, its parent no longer gets the proper wait
result for it:

wait4(-1, [WIFEXITED(s) && WEXITSTATUS(s) == 0], WNOHANG|WUNTRACED, NULL) = 478
wait4(-1, [WIFEXITED(s) && WEXITSTATUS(s) == 0], WNOHANG|WUNTRACED, NULL) = 478
wait4(-1, [WIFEXITED(s) && WEXITSTATUS(s) == 0], WNOHANG|WUNTRACED, NULL) = 478
wait4(-1, [WIFEXITED(s) && WEXITSTATUS(s) == 0], WNOHANG|WUNTRACED, NULL) = 478
wait4(-1, [WIFEXITED(s) && WEXITSTATUS(s) == 0], WNOHANG|WUNTRACED, NULL) = 478
wait4(-1, [WIFEXITED(s) && WEXITSTATUS(s) == 0], WNOHANG|WUNTRACED, NULL) = 478

etc. It is never removed from the list. _TRACEME/exec debugging
appears to have the same problem but it's harder to tell, since one can
not strace GDB in 2.5 without the patch I posted here two weeks ago.
If you don't have a chance to look at this I'll investigate later
today.

--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer
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