Quoting Sukadev Bhattiprolu (sukadev@xxxxxxxxxxxxxxxxxx):
>
> From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> Date: Mon, 16 Feb 2009 12:05:50 -0800
> Subject: [PATCH] Check 'may_checkpoint()' early
>
> We currently check if a task is checkpointable when writing the task
> information to checkpoint file. The small downside of doing this check
> late is that we may have processed several processes in the tree before
> hitting one that cannot be checkpointed.
>
> We anyway walk the process tree we are checkpointing earlier, while
> counting the tasks. We could check if all processes in the tree are
> checkpointable at that time and fail early if any of them are not.
> Since the process tree should be frozen, checking earlier should not
> matter ?
>
> For now, the patch leaves the existing check in cr_write_pids(). We
Yes we'll at least need to add checks that there is no running task
sharing an mm or files_struct with a checkpointed task, else some of
our checks will definately be racy (and are even now).
> can remove that later.
>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> ---
> checkpoint/checkpoint.c | 9 +++++++++
> 1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
> index 64155de..2bbb409 100644
> --- a/checkpoint/checkpoint.c
> +++ b/checkpoint/checkpoint.c
> @@ -347,11 +347,18 @@ static int cr_tree_count_tasks(struct cr_ctx *ctx)
> struct task_struct **tasks_arr = ctx->tasks_arr;
> int tasks_nr = ctx->tasks_nr;
> int nr = 0;
> + int ret;
>
> read_lock(&tasklist_lock);
>
> /* count tasks via DFS scan of the tree */
> while (1) {
> + ret = cr_may_checkpoint_task(task, ctx);
> + if (ret < 0) {
> + nr = ret;
> + break;
> + }
> +
> if (tasks_arr) {
> /* unlikely... but if so then try again later */
> if (nr == tasks_nr) {
> @@ -409,6 +416,8 @@ static int cr_build_tree(struct cr_ctx *ctx)
>
> /* count tasks (no side effects) */
> n = cr_tree_count_tasks(ctx);
> + if (n < 0)
> + return n;
>
> ctx->tasks_nr = n;
> ctx->tasks_arr = kzalloc(n * sizeof(*ctx->tasks_arr), GFP_KERNEL);
> --
> 1.5.2.5
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