Messages in this thread Patch in this message | | | Date | Sat, 4 Dec 2004 14:21:40 -0800 | From | Roland McGrath <> | Subject | [PATCH] fix bogus ECHILD return from wait* with zombie group leader |
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Klaus Dittrich observed this bug and posted a test case for it. This patch fixes both that failure mode and some others possible. What Klaus saw was a false negative (i.e. ECHILD when there was a child) when the group leader was a zombie but delayed because other children live; in the test program this happens in a race between the two threads dying on a signal. The change to the TASK_TRACED case avoids a potential false positive (blocking, or WNOHANG returning 0, when there are really no children left), in the race condition where my_ptrace_child returns zero.
Thanks, Roland
Signed-off-by: Roland McGrath <roland@redhat.com>
--- linux-2.6/kernel/exit.c +++ linux-2.6/kernel/exit.c @@ -1319,6 +1319,10 @@ static long do_wait(pid_t pid, int optio add_wait_queue(¤t->wait_chldexit,&wait); repeat: + /* + * We will set this flag if we see any child that might later + * match our criteria, even if we are not able to reap it yet. + */ flag = 0; current->state = TASK_INTERRUPTIBLE; read_lock(&tasklist_lock); @@ -1337,11 +1341,14 @@ repeat: switch (p->state) { case TASK_TRACED: - flag = 1; if (!my_ptrace_child(p)) continue; /*FALLTHROUGH*/ case TASK_STOPPED: + /* + * It's stopped now, so it might later + * continue, exit, or stop again. + */ flag = 1; if (!(options & WUNTRACED) && !my_ptrace_child(p)) @@ -1377,8 +1384,12 @@ repeat: goto end; break; } - flag = 1; check_continued: + /* + * It's running now, so it might later + * exit, stop, or stop and then continue. + */ + flag = 1; if (!unlikely(options & WCONTINUED)) continue; retval = wait_task_continued( - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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