Re: [RFC][PATCH] fix move/migrate_pages() race on task struct

[Dave Hansen]

On 02/24/2012 09:32 AM, Christoph Lameter wrote:
> @@ -1318,10 +1318,10 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pi
>  	rcu_read_lock();
>  	task = pid ? find_task_by_vpid(pid) : current;
>  	if (!task) {
> -		rcu_read_unlock();
>  		err = -ESRCH;
>  		goto out;
>  	}
...
> +	put_task_struct(task);
> +	task = NULL;
>  	err = do_migrate_pages(mm, old, new,
>  		capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE);
>  out:
> +	if (task)
> +		put_task_struct(task);
> +
>  	if (mm)
>  		mmput(mm);
>  	NODEMASK_SCRATCH_FREE(scratch);

Man, patch did not like this for some reason.  I kept throwing most of
the mempolicy.c hunks away.  I've never seen anything like it.

Anyway...  This looks fine except I think that rcu_read_unlock() need to
stay.  There's currently no release of it after out:.

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