Re: [PATCH] Don't crash if we are self-checkpointing with a child

[Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>]

Thanks -- queued for v23-rc2.

Oren.

On 02/22/2011 02:16 PM, Dan Smith wrote:
> If we are doing a self-checkpoint, we will not be frozen and the
> get_freezer_task() will return NULL.  If we have children, then
> may_checkpoint_task() will attempt to make sure that they are in the
> same cgroup as the freezer task, which will attempt to lock a NULL
> task pointer (and thus go boom).
> 
> This patch just inserts a check before in_same_cgroup_freezer() call
> to make sure we have a freezer task.  The existing check is aimed to
> determine if a task is not frozen alongside the root, so this addition
> catches the case where it is impossible.
> 
> Signed-off-by: Dan Smith <danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> ---
>  kernel/checkpoint/checkpoint.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
> index 0f46acf..33f53e9 100644
> --- a/kernel/checkpoint/checkpoint.c
> +++ b/kernel/checkpoint/checkpoint.c
> @@ -262,8 +262,12 @@ static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
>  	if (t->exit_state)
>  		return 0;
>  
> -	/* verify that all tasks belongs to same freezer cgroup */
> -	if (t != current && !in_same_cgroup_freezer(t, ctx->root_freezer)) {
> +	/*
> +	 * verify that we have a freezer cgroup and that all tasks
> +	 * belong to the same one
> +	 */
> +	if (t != current && (!ctx->root_freezer ||
> +			     !in_same_cgroup_freezer(t, ctx->root_freezer))) {
>  		_ckpt_err(ctx, -EBUSY, "%(T)Not frozen or wrong cgroup\n");
>  		return -EBUSY;
>  	}