Re: [RFC v16][PATCH 19/43] c/r: external checkpoint of a task other than ourself
From: Alexey Dobriyan <hidden>
Date: 2009-05-28 16:33:47
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linux-mm, lkml
On Wed, May 27, 2009 at 06:32:28PM -0400, Oren Laadan wrote:
On Thu, 28 May 2009, Alexey Dobriyan wrote:quoted
On Wed, May 27, 2009 at 01:32:45PM -0400, Oren Laadan wrote:quoted
Now we can do "external" checkpoint, i.e. act on another task.quoted
+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.ood catch. Since all threads share same nsproxy (except those who exits.. duh) we can test for this case, and get the nsproxy from any of the other threads, something like this (untested):
I don't know if such behaviour was intented, but threads have only common pid_ns not whole nsproxy. CLONE_THREAD|CLONE_NEWUTS works just fine.
quoted hunk ↗ jump to hunk
--- a/checkpoint/checkpoint.c +++ b/checkpoint/checkpoint.c@@ -522,9 +522,33 @@ static int get_container(struct ckpt_ctx *ctx, pid_t pid) rcu_read_lock(); nsproxy = task_nsproxy(task); - get_nsproxy(nsproxy); + if (nsproxy) + get_nsproxy(nsproxy); rcu_read_unlock(); + /* + * If we hit a zombie thread-group-leader, nsproxy will be NULL, + * and we instead grab it from one of the other threads. + */ + if (!nsproxy) { + struct task_struct *p = next_thread(task); + + BUG_ON(task->state != TASK_DEAD); + read_lock(&tasklist_lock); + while (p != task && !task_nsproxy(p)) + p = next_thread(p); + nsproxy = get_nsproxy(p); + if (nsproxy) + get_nsproxy(nsproxy); + read_unlock(&tasklist_lock); + } + + /* still not ... too bad ... */ + if (!nsproxy) { + put_task_struct(task); + return -ESRCH; + } + ctx->root_task = task; ctx->root_nsproxy = nsproxy; ctx->root_init = is_container_init(task);
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