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Subject[RFC v16][PATCH 19/43] c/r: external checkpoint of a task other than ourself
Date
Now we can do "external" checkpoint, i.e. act on another task.

sys_checkpoint() now looks up the target pid (in our namespace) and
checkpoints that corresponding task. That task should be the root of
a container, unless CHECKPOINT_SUBTREE flag is given.

sys_restart() remains the same, as the restart is always done in the
context of the restarting task.

Changelog[v16]:
- Use CHECKPOINT_SUBTREE to allow subtree (partial container)

Changelog[v14]:
- Refuse non-self checkpoint if target task isn't frozen

Changelog[v12]:
- Replace obsolete ckpt_debug() with pr_debug()

Changelog[v11]:
- Copy contents of 'init->fs->root' instead of pointing to them

Changelog[v10]:
- Grab vfs root of container init, rather than current process

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
---
checkpoint/checkpoint.c | 79 +++++++++++++++++++++++++++++++++++++-
checkpoint/restart.c | 4 +-
checkpoint/sys.c | 6 +++
include/linux/checkpoint_types.h | 2 +
4 files changed, 87 insertions(+), 4 deletions(-)
diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index a346b7e..086f2d9 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -12,6 +12,9 @@
#define CKPT_DFLAG CKPT_DSYS

#include <linux/version.h>
+#include <linux/sched.h>
+#include <linux/freezer.h>
+#include <linux/ptrace.h>
#include <linux/time.h>
#include <linux/fs.h>
#include <linux/file.h>
@@ -245,23 +248,95 @@ static int checkpoint_write_tail(struct ckpt_ctx *ctx)
return ret;
}

+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);
+ rcu_read_unlock();
+
+ ctx->root_task = task;
+ ctx->root_nsproxy = nsproxy;
+
+ return 0;
+}
+
/* setup checkpoint-specific parts of ctx */
static int init_checkpoint_ctx(struct ckpt_ctx *ctx, pid_t pid)
{
struct fs_struct *fs;
+ int ret;

ctx->root_pid = pid;

+ ret = get_container(ctx, pid);
+ if (ret < 0)
+ return ret;
+
/*
* assume checkpointer is in container's root vfs
* FIXME: this works for now, but will change with real containers
*/

- fs = current->fs;
+ task_lock(ctx->root_task);
+ fs = ctx->root_task->fs;
read_lock(&fs->lock);
ctx->fs_mnt = fs->root;
path_get(&ctx->fs_mnt);
read_unlock(&fs->lock);
+ task_unlock(ctx->root_task);

return 0;
}
@@ -276,7 +351,7 @@ int do_checkpoint(struct ckpt_ctx *ctx, pid_t pid)
ret = checkpoint_write_header(ctx);
if (ret < 0)
goto out;
- ret = checkpoint_task(ctx, current);
+ ret = checkpoint_task(ctx, ctx->root_task);
if (ret < 0)
goto out;
ret = checkpoint_write_tail(ctx);
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index d3d6c5e..ca33539 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -352,7 +352,7 @@ static int restore_read_tail(struct ckpt_ctx *ctx)
}

/* setup restart-specific parts of ctx */
-static int init_restart_ctx(struct ckpt_ctx *ctx)
+static int init_restart_ctx(struct ckpt_ctx *ctx, pid_t pid)
{
return 0;
}
@@ -361,7 +361,7 @@ int do_restart(struct ckpt_ctx *ctx, pid_t pid)
{
int ret;

- ret = init_restart_ctx(ctx);
+ ret = init_restart_ctx(ctx, pid);
if (ret < 0)
return ret;
ret = restore_read_header(ctx);
diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index 7bf70e4..c809120 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -12,6 +12,7 @@
#define CKPT_DFLAG CKPT_DSYS

#include <linux/sched.h>
+#include <linux/nsproxy.h>
#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/fs.h>
@@ -173,6 +174,11 @@ static void ckpt_ctx_free(struct ckpt_ctx *ctx)
path_put(&ctx->fs_mnt);
ckpt_pgarr_free(ctx);

+ if (ctx->root_nsproxy)
+ put_nsproxy(ctx->root_nsproxy);
+ if (ctx->root_task)
+ put_task_struct(ctx->root_task);
+
kfree(ctx);
}

diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
index a0ea5f6..4369f90 100644
--- a/include/linux/checkpoint_types.h
+++ b/include/linux/checkpoint_types.h
@@ -28,6 +28,8 @@ struct ckpt_ctx {
int crid; /* unique checkpoint id */

pid_t root_pid; /* container identifier */
+ struct task_struct *root_task; /* container root task */
+ struct nsproxy *root_nsproxy; /* container root nsproxy */

unsigned long kflags; /* kerenl flags */
unsigned long uflags; /* user flags */
--
1.6.0.4


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