Re: [PATCH] SUNRPC/cache: Allow garbage collection of invalid cache entries

[bfields@fieldses.org (J. Bruce Fields)]

On Tue, Jan 14, 2020 at 11:57:38AM -0500, Trond Myklebust wrote:
> If the cache entry never gets initialised, we want the garbage
> collector to be able to evict it. Otherwise if the upcall daemon
> fails to initialise the entry, we end up never expiring it.

Could you tell us more about what motivated this?

It's causing failures on pynfs server-reboot tests.  I haven't pinned
down the cause yet, but it looks like it could be a regression to the
behavior Kinglong Mee describes in detail in his original patch.

Dropping for the time being.

--b.

> 
> Fixes: d6fc8821c2d2 ("SUNRPC/Cache: Always treat the invalid cache as unexpired")
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  include/linux/sunrpc/cache.h |  3 ---
>  net/sunrpc/cache.c           | 36 +++++++++++++++++++-----------------
>  2 files changed, 19 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
> index f8603724fbee..0428dd23fd79 100644
> --- a/include/linux/sunrpc/cache.h
> +++ b/include/linux/sunrpc/cache.h
> @@ -202,9 +202,6 @@ static inline void cache_put(struct cache_head *h, struct cache_detail *cd)
>  
>  static inline bool cache_is_expired(struct cache_detail *detail, struct cache_head *h)
>  {
> -	if (!test_bit(CACHE_VALID, &h->flags))
> -		return false;
> -
>  	return  (h->expiry_time < seconds_since_boot()) ||
>  		(detail->flush_time >= h->last_refresh);
>  }
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index 52d927210d32..99d630150af6 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -65,13 +65,14 @@ static struct cache_head *sunrpc_cache_find_rcu(struct cache_detail *detail,
>  
>  	rcu_read_lock();
>  	hlist_for_each_entry_rcu(tmp, head, cache_list) {
> -		if (detail->match(tmp, key)) {
> -			if (cache_is_expired(detail, tmp))
> -				continue;
> -			tmp = cache_get_rcu(tmp);
> -			rcu_read_unlock();
> -			return tmp;
> -		}
> +		if (!detail->match(tmp, key))
> +			continue;
> +		if (test_bit(CACHE_VALID, &tmp->flags) &&
> +		    cache_is_expired(detail, tmp))
> +			continue;
> +		tmp = cache_get_rcu(tmp);
> +		rcu_read_unlock();
> +		return tmp;
>  	}
>  	rcu_read_unlock();
>  	return NULL;
> @@ -114,17 +115,18 @@ static struct cache_head *sunrpc_cache_add_entry(struct cache_detail *detail,
>  
>  	/* check if entry appeared while we slept */
>  	hlist_for_each_entry_rcu(tmp, head, cache_list) {
> -		if (detail->match(tmp, key)) {
> -			if (cache_is_expired(detail, tmp)) {
> -				sunrpc_begin_cache_remove_entry(tmp, detail);
> -				freeme = tmp;
> -				break;
> -			}
> -			cache_get(tmp);
> -			spin_unlock(&detail->hash_lock);
> -			cache_put(new, detail);
> -			return tmp;
> +		if (!detail->match(tmp, key))
> +			continue;
> +		if (test_bit(CACHE_VALID, &tmp->flags) &&
> +		    cache_is_expired(detail, tmp)) {
> +			sunrpc_begin_cache_remove_entry(tmp, detail);
> +			freeme = tmp;
> +			break;
>  		}
> +		cache_get(tmp);
> +		spin_unlock(&detail->hash_lock);
> +		cache_put(new, detail);
> +		return tmp;
>  	}
>  
>  	hlist_add_head_rcu(&new->cache_list, head);
> -- 
> 2.24.1