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SubjectRe: [RFC v16][PATCH 19/43] c/r: external checkpoint of a task other than ourself
On Wed, May 27, 2009 at 01:32:45PM -0400, Oren Laadan wrote:
> Now we can do "external" checkpoint, i.e. act on another task.

> +static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
> +{
> + if (t->state == TASK_DEAD) {
> + pr_warning("c/r: task %d is TASK_DEAD\n", task_pid_vnr(t));
> + return -EAGAIN;
> + }
> +
> + if (!ptrace_may_access(t, PTRACE_MODE_READ)) {
> + __ckpt_write_err(ctx, "access to task %d (%s) denied",
> + task_pid_vnr(t), t->comm);
> + return -EPERM;
> + }
> +
> + /* verify that the task is frozen (unless self) */
> + if (t != current && !frozen(t)) {
> + __ckpt_write_err(ctx, "task %d (%s) is not frozen",
> + task_pid_vnr(t), t->comm);
> + return -EBUSY;
> + }
> +
> + /* FIX: add support for ptraced tasks */
> + if (task_ptrace(t)) {
> + __ckpt_write_err(ctx, "task %d (%s) is ptraced",
> + task_pid_vnr(t), t->comm);
> + return -EBUSY;
> + }
> +
> + return 0;
> +}
> +
> +static int get_container(struct ckpt_ctx *ctx, pid_t pid)
> +{
> + struct task_struct *task = NULL;
> + struct nsproxy *nsproxy = NULL;
> + int ret;
> +
> + ctx->root_pid = pid;
> +
> + read_lock(&tasklist_lock);
> + task = find_task_by_vpid(pid);
> + if (task)
> + get_task_struct(task);
> + read_unlock(&tasklist_lock);
> +
> + if (!task)
> + return -ESRCH;
> +
> + ret = may_checkpoint_task(ctx, task);
> + if (ret) {
> + ckpt_write_err(ctx, NULL);
> + put_task_struct(task);
> + return ret;
> + }
> +
> + rcu_read_lock();
> + nsproxy = task_nsproxy(task);
> + get_nsproxy(nsproxy);

Will oops if init is multi-threaded and thread group leader exited
(nsproxy = NULL). I need to think what to do, too.

> + rcu_read_unlock();
> +
> + ctx->root_task = task;
> + ctx->root_nsproxy = nsproxy;
> +
> + return 0;
> +}


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