Introduce a helper to iterate over the descendants of a given
task. The prototype is:
int walk_task_subtree(struct task_struct *root,
int (*func)(struct task_struct *, void *),
void *data)
The function will start with @root, and iterate through all the
descendants, including threads, in a DFS manner. Children of a task
are traversed before proceeding to the next thread of that task.
For each task, the callback @func will be called providing the task
pointer and the @data. The callback is invoked while holding the
tasklist_lock for reading. If the callback fails it should return a
negative error, and the traversal ends. If the callback succeeds, it
returns a non-negative number, and these values are summed.
On success, walk_task_subtree() returns the total summed. On failure,
it returns a negative value.
The code in checkpoint/checkpoint.c and checkpoint/restart.c has
been converted to use this helper.
Signed-off-by: Oren Laadan <orenl@xxxxxxxxxxxxxxx>
---
checkpoint/checkpoint.c | 97 ++++++++++++++--------------------------
checkpoint/restart.c | 105 +++++++++++++++++++-------------------------
checkpoint/sys.c | 55 +++++++++++++++++++++++
include/linux/checkpoint.h | 3 +
4 files changed, 137 insertions(+), 123 deletions(-)
diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
index dbe9e10..1eeb557 100644
--- a/checkpoint/checkpoint.c
+++ b/checkpoint/checkpoint.c
@@ -520,80 +520,51 @@ static int collect_objects(struct ckpt_ctx *ctx)
return ret;
}
+struct ckpt_cnt_tasks {
+ struct ckpt_ctx *ctx;
+ int nr;
+};
+
/* count number of tasks in tree (and optionally fill pid's in array) */
-static int tree_count_tasks(struct ckpt_ctx *ctx)
+static int __tree_count_tasks(struct task_struct *task, void *data)
{
- struct task_struct *root;
- struct task_struct *task;
- struct task_struct *parent;
- struct task_struct **tasks_arr = ctx->tasks_arr;
- int nr_tasks = ctx->nr_tasks;
- int nr = 0;
+ struct ckpt_cnt_tasks *d = (struct ckpt_cnt_tasks *) data;
+ struct ckpt_ctx *ctx = d->ctx;
int ret;
- read_lock(&tasklist_lock);
-
- /* we hold the lock, so root_task->real_parent can't change */
- task = ctx->root_task;
- if (ctx->root_init) {
- /* container-init: start from container parent */
- parent = task->real_parent;
- root = parent;
- } else {
- /* non-container-init: start from root task and down */
- parent = NULL;
- root = task;
- }
-
- /* count tasks via DFS scan of the tree */
- while (1) {
- ctx->tsk = task; /* (for ckpt_write_err) */
+ ctx->tsk = task; /* (for ckpt_write_err) */
- /* is this task cool ? */
- ret = may_checkpoint_task(ctx, task);
- if (ret < 0) {
- nr = ret;
- break;
- }
- if (tasks_arr) {
- /* unlikely... but if so then try again later */
- if (nr == nr_tasks) {
- nr = -EBUSY; /* cleanup in ckpt_ctx_free() */
- break;
- }
- tasks_arr[nr] = task;
- get_task_struct(task);
- }
- nr++;
- /* if has children - proceed with child */
- if (!list_empty(&task->children)) {
- parent = task;
- task = list_entry(task->children.next,
- struct task_struct, sibling);
- continue;
- }
- while (task != root) {
- /* if has sibling - proceed with sibling */
- if (!list_is_last(&task->sibling, &parent->children)) {
- task = list_entry(task->sibling.next,
- struct task_struct, sibling);
- break;
- }
+ /* is this task cool ? */
+ ret = may_checkpoint_task(ctx, task);
+ if (ret < 0)
+ goto out;
- /* else, trace back to parent and proceed */
- task = parent;
- parent = parent->real_parent;
+ if (ctx->tasks_arr) {
+ if (d->nr == ctx->nr_tasks) { /* unlikely... try again later */
+ __ckpt_write_err(ctx, "TE", "bad task count\n", -EBUSY);
+ ret = -EBUSY;
+ goto out;
}
- if (task == root)
- break;
+ ctx->tasks_arr[d->nr++] = task;
+ get_task_struct(task);
}
+
+ ret = 1;
+ out:
+ if (ret < 0)
+ ckpt_write_err(ctx, "", NULL);
ctx->tsk = NULL;
+ return ret;
+}
- read_unlock(&tasklist_lock);
+static int tree_count_tasks(struct ckpt_ctx *ctx)
+{
+ struct ckpt_cnt_tasks data;
- if (nr < 0)
- ckpt_write_err(ctx, "", NULL);
- return nr;
+ data.ctx = ctx;
+ data.nr = 0;
+
+ return walk_task_subtree(ctx->root_task, __tree_count_tasks, &data);
}
/*
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index 37454c5..c021eaf 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -804,77 +804,56 @@ static int do_restore_task(void)
* Called by the coodinator to set the ->checkpoint_ctx pointer of the
* root task and all its descendants.
*/
-static int prepare_descendants(struct ckpt_ctx *ctx, struct task_struct *root)
+static int __prepare_descendants(struct task_struct *task, void *data)
{
- struct task_struct *leader = root;
- struct task_struct *parent = NULL;
- struct task_struct *task = root;
- int nr_pids = 0;
- int ret = -EBUSY;
+ struct ckpt_ctx *ctx = (struct ckpt_ctx *) data;
- read_lock(&tasklist_lock);
- while (1) {
- ckpt_debug("consider task %d\n", task_pid_vnr(task));
- if (task_ptrace(task) & PT_PTRACED)
- break;
- /*
- * Set task->checkpoint_ctx of all non-zombie descendants.
- * If a descendant already has a ->checkpoint_ctx, it
- * must be a coordinator (for a different restart ?) so
- * we fail.
- *
- * Note that own ancestors cannot interfere since they
- * won't descend past us, as own ->checkpoint_ctx must
- * already be set.
- */
- if (!task->exit_state) {
- if (!set_task_ctx(task, ctx))
- break;
- ckpt_debug("prepare task %d\n", task_pid_vnr(task));
- wake_up_process(task);
- nr_pids++;
- }
+ ckpt_debug("consider task %d\n", task_pid_vnr(task));
- /* if has children - proceed with child */
- if (!list_empty(&task->children)) {
- parent = task;
- task = list_entry(task->children.next,
- struct task_struct, sibling);
- continue;
- }
- while (task != root) {
- /* if has sibling - proceed with sibling */
- if (!list_is_last(&task->sibling, &parent->children)) {
- task = list_entry(task->sibling.next,
- struct task_struct, sibling);
- break;
- }
-
- /* else, trace back to parent and proceed */
- task = parent;
- parent = parent->real_parent;
- }
- if (task == root) {
- /* in case root task is multi-threaded */
- root = task = next_thread(task);
- if (root == leader) {
- ret = 0;
- break;
- }
- }
+ if (task_ptrace(task) & PT_PTRACED) {
+ ckpt_debug("ptraced task %d\n", task_pid_vnr(task));
+ return -EBUSY;
}
- read_unlock(&tasklist_lock);
- ckpt_debug("nr %d/%d ret %d\n", ctx->nr_pids, nr_pids, ret);
+
+ /*
+ * Set task->checkpoint_ctx of all non-zombie descendants.
+ * If a descendant already has a ->checkpoint_ctx, it
+ * must be a coordinator (for a different restart ?) so
+ * we fail.
+ *
+ * Note that own ancestors cannot interfere since they
+ * won't descend past us, as own ->checkpoint_ctx must
+ * already be set.
+ */
+ if (!task->exit_state) {
+ if (!set_task_ctx(task, ctx))
+ return -EBUSY;
+ ckpt_debug("prepare task %d\n", task_pid_vnr(task));
+ wake_up_process(task);
+ return 1;
+ }
+
+ return 0;
+}
+
+static int prepare_descendants(struct ckpt_ctx *ctx, struct task_struct *root)
+{
+ int nr_pids;
+
+ nr_pids = walk_task_subtree(root, __prepare_descendants, ctx);
+ ckpt_debug("nr %d/%d\n", ctx->nr_pids, nr_pids);
+ if (nr_pids < 0)
+ return nr_pids;
/*
* Actual tasks count may exceed ctx->nr_pids due of 'dead'
* tasks used as place-holders for PGIDs, but not fall short.
*/
- if (!ret && (nr_pids < ctx->nr_pids))
- ret = -ESRCH;
+ if (nr_pids < ctx->nr_pids)
+ return -ESRCH;
atomic_set(&ctx->nr_total, nr_pids);
- return ret;
+ return nr_pids;
}
static int wait_all_tasks_finish(struct ckpt_ctx *ctx)
@@ -991,6 +970,12 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid)
return -EBUSY;
}
+ /*
+ * From now on we are committed to the restart. If anything
+ * fails, we'll wipe out the entire subtree below us, to
+ * ensure proper cleanup.
+ */
+
if (ctx->uflags & RESTART_TASKSELF) {
ret = restore_task(ctx);
ckpt_debug("restore task: %d\n", ret);
diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index 77613d7..7604089 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -276,6 +276,61 @@ void ckpt_ctx_put(struct ckpt_ctx *ctx)
ckpt_ctx_free(ctx);
}
+int walk_task_subtree(struct task_struct *root,
+ int (*func)(struct task_struct *, void *),
+ void *data)
+{
+
+ struct task_struct *leader = root;
+ struct task_struct *parent = NULL;
+ struct task_struct *task = root;
+ int total = 0;
+ int ret;
+
+ read_lock(&tasklist_lock);
+ while (1) {
+ /* invoke callback on this task */
+ ret = func(task, data);
+ if (ret < 0)
+ break;
+
+ total += ret;
+
+ /* if has children - proceed with child */
+ if (!list_empty(&task->children)) {
+ parent = task;
+ task = list_entry(task->children.next,
+ struct task_struct, sibling);
+ continue;
+ }
+
+ while (task != root) {
+ /* if has sibling - proceed with sibling */
+ if (!list_is_last(&task->sibling, &parent->children)) {
+ task = list_entry(task->sibling.next,
+ struct task_struct, sibling);
+ break;
+ }
+
+ /* else, trace back to parent and proceed */
+ task = parent;
+ parent = parent->real_parent;
+ }
+
+ if (task == root) {
+ /* in case root task is multi-threaded */
+ root = task = next_thread(task);
+ if (root == leader)
+ break;
+ }
+ }
+ read_unlock(&tasklist_lock);
+
+ ckpt_debug("total %d ret %d\n", total, ret);
+ return (ret < 0 ? ret : total);
+}
+
+
/**
* sys_checkpoint - checkpoint a container
* @pid: pid of the container init(1) process
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index b7f1796..12210e4 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -50,6 +50,9 @@
RESTART_FROZEN | \
RESTART_GHOST)
+extern int walk_task_subtree(struct task_struct *task,
+ int (*func)(struct task_struct *, void *),
+ void *data);
extern void exit_checkpoint(struct task_struct *tsk);
extern int ckpt_kwrite(struct ckpt_ctx *ctx, void *buf, int count);
--
1.6.0.4
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