[Devel] Re: [patch 2/3][NETNS45][V2] make timewait unhash lock free

[Denis V. Lunev]

Sorry for a delay in answer. A was ill last three days.
Some stylistic comments inside

Daniel Lezcano wrote:
> From: Daniel Lezcano <dlezcano at fr.ibm.com>
> 
> The network namespace cleanup will remove all timewait sockets
> related to it because there are pointless. 
> 
> The problem is we need to browse the established hash table and 
> for that we need to take the lock. For each timesocket we call 
> inet_deschedule and this one take the established hash table lock
> too.
> 
> The following patchset split the removing of the established hash
> into two parts, one removing the node from the hash and another
> taking the lock and calling the first one.
> 
> The network namespace cleanup can be done calling the lock free
> function.
> 
> Signed-off-by: Daniel Lezcano <dlezcano at fr.ibm.com>
> ---
>  include/net/inet_timewait_sock.h |   13 ++++++++++++
>  net/ipv4/inet_timewait_sock.c    |   40 +++++++++++++++++++++++++++------------
>  2 files changed, 41 insertions(+), 12 deletions(-)
> 
> Index: linux-2.6-netns/net/ipv4/inet_timewait_sock.c
> ===================================================================
> --- linux-2.6-netns.orig/net/ipv4/inet_timewait_sock.c
> +++ linux-2.6-netns/net/ipv4/inet_timewait_sock.c
> @@ -13,25 +13,28 @@
>  #include <net/inet_timewait_sock.h>
>  #include <net/ip.h>
>  
> -/* Must be called with locally disabled BHs. */
> -static void __inet_twsk_kill(struct inet_timewait_sock *tw,
> -			     struct inet_hashinfo *hashinfo)
> +static inline int inet_twsk_unehash(struct inet_timewait_sock *tw,
> +				    struct inet_hashinfo *hashinfo)
>  {
> -	struct inet_bind_hashbucket *bhead;
> -	struct inet_bind_bucket *tb;
> -	/* Unlink from established hashes. */
> -	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, tw->tw_hash);
> +	struct inet_ehash_bucket *ehead =
> +		inet_ehash_bucket(hashinfo, tw->tw_hash);
>  
>  	write_lock(&ehead->lock);
> -	if (hlist_unhashed(&tw->tw_node)) {
> +	if (__inet_twsk_unehash(tw)) {
>  		write_unlock(&ehead->lock);
> -		return;
> +		return 1;
>  	}
> -	__hlist_del(&tw->tw_node);
> -	sk_node_init(&tw->tw_node);
>  	write_unlock(&ehead->lock);
>  
> -	/* Disassociate with bind bucket. */
> +	return 0;
> +}
as far as I can understand the code, it will look better as below

struct inet_ehash_bucket *ehead =
    inet_ehash_bucket(hashinfo, tw->tw_hash);
int ret;

write_lock(&ehead->lock);
ret = __inet_twsk_unehash(tw);
write_unlock(&ehead->lock);
return ret;


> +
> +void inet_twsk_unbhash(struct inet_timewait_sock *tw,
> +		       struct inet_hashinfo *hashinfo)
> +{
> +	struct inet_bind_hashbucket *bhead;
> +	struct inet_bind_bucket *tb;
> +
>  	bhead = &hashinfo->bhash[inet_bhashfn(tw->tw_net, tw->tw_num, hashinfo->bhash_size)];
>  	spin_lock(&bhead->lock);
>  	tb = tw->tw_tb;
> @@ -39,6 +42,19 @@ static void __inet_twsk_kill(struct inet
>  	tw->tw_tb = NULL;
>  	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
>  	spin_unlock(&bhead->lock);
> +}
> +
> +/* Must be called with locally disabled BHs. */
> +static void __inet_twsk_kill(struct inet_timewait_sock *tw,
> +			     struct inet_hashinfo *hashinfo)
> +{
> +	/* Unlink from established hashes. */
> +	if (inet_twsk_unehash(tw, hashinfo))
> +		return;
> +
> +	/* Disassociate with bind bucket. */
> +	inet_twsk_unbhash(tw, hashinfo);
> +
>  #ifdef SOCK_REFCNT_DEBUG
>  	if (atomic_read(&tw->tw_refcnt) != 1) {
>  		printk(KERN_DEBUG "%s timewait_sock %p refcnt=%d\n",
> Index: linux-2.6-netns/include/net/inet_timewait_sock.h
> ===================================================================
> --- linux-2.6-netns.orig/include/net/inet_timewait_sock.h
> +++ linux-2.6-netns/include/net/inet_timewait_sock.h
> @@ -173,6 +173,19 @@ static inline int inet_twsk_del_dead_nod
>  	return 0;
>  }
>  
> +static inline int __inet_twsk_unehash(struct inet_timewait_sock *tw)
> +{
> +	if (hlist_unhashed(&tw->tw_node))
> +		return 1;
> +	__hlist_del(&tw->tw_node);
> +	sk_node_init(&tw->tw_node);
> +
>> see above about inet_twsk_unehash. We should insert
        /* Disassociate with bind bucket. */
>> here
> +	return 0;
> +}
> +
> +extern void inet_twsk_unbhash(struct inet_timewait_sock *tw,
> +			      struct inet_hashinfo *hashinfo);
> +
>  #define inet_twsk_for_each(tw, node, head) \
>  	hlist_for_each_entry(tw, node, head, tw_node)
>  
> 

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