Messages in this thread | | | Date | Sun, 14 Dec 2003 06:25:16 +0100 | From | Petr Vandrovec <> | Subject | Problem with exiting threads under NPTL |
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Hi, several times one of our threads ended up as ZOMBIE and nobody wants to pick him up - even init ignores it. Inspection of kernel structures revealed that task's exit code is 0, exit_signal is -1, ptrace is 0 and state is 8 (ZOMBIE).
Quick look at exit_notify reveals that it should not happen: if task has exit_signal == -1 and is not ptraced, we should immediate move to TASK_DEAD and get rid of task as fast as possible.
But problem is that in do_notify_parent we have code which sets exit_signal to -1 if parent ignores SIGCHLD, and we call do_notify_parent() for group leader from release_task() when last member of thread group exits, without taking any care about eventual changes in exit_signal field.
So if some process ignores SIGCHLD, and spawns child process which creates additional thread, and main thread in child exits before child it created, you'll end up with immortal zombie.
Best regards, Petr Vandrovec vandrove@vc.cvut.cz
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND 5 0 3709 1 15 0 0 0 exit Z tty3 0:00 [test] <defunct>
Creator of immortal zombies:
#include <pthread.h> #include <signal.h> #include <unistd.h> #include <stdio.h>
static void* thread(void* dummy) { /* Make sure that we exit as second thread */ sleep(1); return NULL; }
void main(void) { int pid;
signal(SIGCHLD, SIG_IGN);
pid = fork(); if (pid == 0) { pthread_t p;
pthread_create(&p, NULL, thread, NULL); } else { /* Sleep some time so we know that child threads exit before us */ sleep(2); printf("Look for task %d...\n", pid); } }
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