Re: [PATCH 2/2] SUNRPC: Drop all entries from cache_detail when cache_purge()

[NeilBrown <neilb@suse.com>]

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On Mon, Feb 06 2017, Kinglong Mee wrote:

> User always free the cache_detail after sunrpc_destroy_cache_detail(),
> so, it must cleanup up entries that left in the cache_detail,
> otherwise, NULL reference may be caused when using the left entries.
>
> Also, NeriBrown suggests "write a stand-alone cache_purge()."
>
> v2, a stand-alone cache_purge(), not only for sunrpc_destroy_cache_detail
>
> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
> ---
>  net/sunrpc/cache.c | 39 ++++++++++++++++++++++++---------------
>  1 file changed, 24 insertions(+), 15 deletions(-)
>
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index 8147e8d..bd6ee79 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -362,11 +362,6 @@ void sunrpc_destroy_cache_detail(struct cache_detail *cd)
>  	cache_purge(cd);
>  	spin_lock(&cache_list_lock);
>  	write_lock(&cd->hash_lock);
> -	if (cd->entries) {
> -		write_unlock(&cd->hash_lock);
> -		spin_unlock(&cache_list_lock);
> -		goto out;
> -	}
>  	if (current_detail == cd)
>  		current_detail = NULL;
>  	list_del_init(&cd->others);
> @@ -376,9 +371,6 @@ void sunrpc_destroy_cache_detail(struct cache_detail *cd)
>  		/* module must be being unloaded so its safe to kill the worker */
>  		cancel_delayed_work_sync(&cache_cleaner);
>  	}
> -	return;
> -out:
> -	printk(KERN_ERR "RPC: failed to unregister %s cache\n", cd->name);
>  }
>  EXPORT_SYMBOL_GPL(sunrpc_destroy_cache_detail);
>  
> @@ -497,13 +489,30 @@ EXPORT_SYMBOL_GPL(cache_flush);
>  
>  void cache_purge(struct cache_detail *detail)
>  {
> -	time_t now = seconds_since_boot();
> -	if (detail->flush_time >= now)
> -		now = detail->flush_time + 1;
> -	/* 'now' is the maximum value any 'last_refresh' can have */
> -	detail->flush_time = now;
> -	detail->nextcheck = seconds_since_boot();
> -	cache_flush();
> +	struct cache_head *ch = NULL;
> +	struct hlist_head *head = NULL;
> +	struct hlist_node *tmp = NULL;
> +	int i = 0;
> +
> +	write_lock(&detail->hash_lock);
> +	if (!detail->entries) {
> +		write_unlock(&detail->hash_lock);
> +		return;
> +	}
> +
> +	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
> +	for (i = 0; i < detail->hash_size; i++) {
> +		head = &detail->hash_table[i];
> +		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
> +			hlist_del_init(&ch->cache_list);
> +			detail->entries--;
> +
> +			set_bit(CACHE_CLEANED, &ch->flags);
> +			cache_fresh_unlocked(ch, detail);
> +			cache_put(ch, detail);

I'm a little bothered by calling cache_fresh_unlocked() while holding
->hash_lock.  No other code does that.
You could probably argue that we don't need ->hash_lock at all here
because by the time we call cache_purge(), there cannot safely be any
other users.  Should we just drop the write_lock() call?

NeilBrown


> +		}
> +	}
> +	write_unlock(&detail->hash_lock);
>  }
>  EXPORT_SYMBOL_GPL(cache_purge);
>  
> -- 
> 2.9.3
>
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