Messages in this thread Patch in this message | | | Date | Wed, 15 Feb 2006 22:13:26 +0300 | From | Oleg Nesterov <> | Subject | [PATCH 2/2] fix kill_proc_info() vs fork() theoretical race |
| |
copy_process:
attach_pid(p, PIDTYPE_PID, p->pid); attach_pid(p, PIDTYPE_TGID, p->tgid);
What if kill_proc_info(p->pid) happens in between?
copy_process() holds current->sighand.siglock, so we are safe in CLONE_THREAD case, because current->sighand == p->sighand.
Otherwise, p->sighand is unlocked, the new process is already visible to the find_task_by_pid(), but have a copy of parent's 'struct pid' in ->pids[PIDTYPE_TGID].
This means that __group_complete_signal() may hang while doing
do ... while (next_thread() != p)
We can solve this problem if we reverse these 2 attach_pid()s:
attach_pid() does wmb()
group_send_sig_info() calls spin_lock(), which provides a read barrier. // Yes ?
I don't think we can hit this race in practice, but still.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 2.6.16-rc3/kernel/fork.c~2_HANG 2006-02-15 23:21:51.000000000 +0300 +++ 2.6.16-rc3/kernel/fork.c 2006-02-16 00:03:20.000000000 +0300 @@ -1173,8 +1173,6 @@ static task_t *copy_process(unsigned lon if (unlikely(p->ptrace & PT_PTRACED)) __ptrace_link(p, current->parent); - attach_pid(p, PIDTYPE_PID, p->pid); - attach_pid(p, PIDTYPE_TGID, p->tgid); if (thread_group_leader(p)) { p->signal->tty = current->signal->tty; p->signal->pgrp = process_group(current); @@ -1184,6 +1182,8 @@ static task_t *copy_process(unsigned lon if (p->pid) __get_cpu_var(process_counts)++; } + attach_pid(p, PIDTYPE_TGID, p->tgid); + attach_pid(p, PIDTYPE_PID, p->pid); nr_threads++; total_forks++; - 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/
| |