Oleg Nesterov
eac1b5e57d
ptrace: do_wait(traced_leader_killed_by_mt_exec) can block forever ...
Test-case:
void *tfunc(void *arg)
{
execvp("true", NULL);
return NULL;
}
int main(void)
{
int pid;
if (fork()) {
pthread_t t;
kill(getpid(), SIGSTOP);
pthread_create(&t, NULL, tfunc, NULL);
for (;;)
pause();
}
pid = getppid();
assert(ptrace(PTRACE_ATTACH, pid, 0,0) == 0);
while (wait(NULL) > 0)
ptrace(PTRACE_CONT, pid, 0,0);
return 0;
}
It is racy, exit_notify() does __wake_up_parent() too. But in the
likely case it triggers the problem: de_thread() does release_task()
and the old leader goes away without the notification, the tracer
sleeps in do_wait() without children/tracees.
Change de_thread() to do __wake_up_parent(traced_leader->parent).
Since it is already EXIT_DEAD we can do this without ptrace_unlink(),
EXIT_DEAD threads do not exist from do_wait's pov.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
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