[CRIU] Re: [RFC PATCH] posix timers: allocate timer id per task

[Pavel Emelyanov]

On 10/15/2012 06:01 PM, Stanislav Kinsbursky wrote:
> This patch replaces global idr with global hash table for posix timers and
> makes timer ids unique not globally, but per task. Next free timer id is type
> of integer and stored on signal struct (posix_timer_id). If free timer id
> reaches negative value on timer creation, it will be dropped to zero and
> -EAGAIN will be returned to user.
> 
> Hash table is size of page (4KB).
> 
> Key is constructed as follows:
> key = hash_ptr(current->signal) ^ hash_32(posix_timer_id);
> 
> ---
>  include/linux/posix-timers.h |    1 
>  include/linux/sched.h        |    4 +-
>  kernel/posix-timers.c        |  112 ++++++++++++++++++++++++++++--------------
>  3 files changed, 78 insertions(+), 39 deletions(-)
> 


> +{
> +	struct signal_struct *sig = current->signal;
> +	struct hlist_head *head;
> +	int ret = -ENOENT;
> +
> +	do {
> +		spin_lock(&hash_lock);
> +		head = &posix_timers_hashtable[hash(sig, sig->posix_timer_id)];
> +		if (__posix_timers_find(head, sig, sig->posix_timer_id) == NULL) {
> +			hlist_add_head(&timer->t_hash, head);
> +			ret = sig->posix_timer_id++;
> +		} else if (++sig->posix_timer_id < 0) {
> +			sig->posix_timer_id = 0;
> +			ret = -EAGAIN;

What for? Overflow is OK, no need in restart.

> +		}
> +		spin_unlock(&hash_lock);
> +	} while (ret == -ENOENT);
> +	return ret;
> +}