Re: [PATCH] sunrpc: clean-up cache downcall

From: Chuck Lever <chuck.lever@oracle.com>
To: Roberto Bergantinos Corpas <rbergant@redhat.com>
Cc: Bruce Fields <bfields@fieldses.org>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH] sunrpc: clean-up cache downcall
Date: Fri, 27 Nov 2020 11:50:46 -0500	[thread overview]
Message-ID: <F08098E1-7E04-4ECA-852A-C93E837E4EBF@oracle.com> (raw)
In-Reply-To: <20201127161451.17922-1-rbergant@redhat.com>

Hi Roberto-

I spotted some mechanical problems.

> On Nov 27, 2020, at 11:14 AM, Roberto Bergantinos Corpas <rbergant@redhat.com> wrote:
> 
> We can simplifly code around cache_downcall unifying memory

^simplifly^simplify

> allocations using kvmalloc, this have the benefit of getting rid of

^, this have^. This has

> cache_slow_downcall (and queue_io_mutex), and also matches userland
> allocation size and limits
> 
> Signed-off-by: Roberto Bergantinos Corpas <rbergant@redhat.com>

Assuming Bruce is copacetic with this patch, the change looks
appropriate for the v5.11 merge window. However, this patch
doesn't appear to apply to v5.10-rc5. Might be because
27a1e8a0f79e ("sunrpc: raise kernel RPC channel buffer size")
was already merged?

> ---
> net/sunrpc/cache.c | 41 +++++++++++------------------------------
> 1 file changed, 11 insertions(+), 30 deletions(-)
> 
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index baef5ee43dbb..1347ecae9c84 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -777,7 +777,6 @@ void cache_clean_deferred(void *owner)
>  */
> 
> static DEFINE_SPINLOCK(queue_lock);
> -static DEFINE_MUTEX(queue_io_mutex);
> 
> struct cache_queue {
> 	struct list_head	list;
> @@ -905,44 +904,26 @@ static ssize_t cache_do_downcall(char *kaddr, const char __user *buf,
> 	return ret;
> }
> 
> -static ssize_t cache_slow_downcall(const char __user *buf,
> -				   size_t count, struct cache_detail *cd)
> -{
> -	static char write_buf[8192]; /* protected by queue_io_mutex */
> -	ssize_t ret = -EINVAL;
> -
> -	if (count >= sizeof(write_buf))
> -		goto out;
> -	mutex_lock(&queue_io_mutex);
> -	ret = cache_do_downcall(write_buf, buf, count, cd);
> -	mutex_unlock(&queue_io_mutex);
> -out:
> -	return ret;
> -}
> -
> static ssize_t cache_downcall(struct address_space *mapping,
> 			      const char __user *buf,
> 			      size_t count, struct cache_detail *cd)
> {
> -	struct page *page;
> -	char *kaddr;
> +	char *write_buf;
> 	ssize_t ret = -ENOMEM;
> 
> -	if (count >= PAGE_SIZE)
> -		goto out_slow;
> +	if (count >= 32768) { /* 32k is max userland buffer, lets check anyway */
> +		ret = -EINVAL;
> +		goto out;
> +	}
> 
> -	page = find_or_create_page(mapping, 0, GFP_KERNEL);
> -	if (!page)
> -		goto out_slow;
> +	write_buf = kvmalloc(count + 1, GFP_KERNEL);
> +	if (!write_buf)
> +		goto out;
> 
> -	kaddr = kmap(page);
> -	ret = cache_do_downcall(kaddr, buf, count, cd);
> -	kunmap(page);
> -	unlock_page(page);
> -	put_page(page);
> +	ret = cache_do_downcall(write_buf, buf, count, cd);
> +	kvfree(write_buf);
> +out:
> 	return ret;
> -out_slow:
> -	return cache_slow_downcall(buf, count, cd);
> }
> 
> static ssize_t cache_write(struct file *filp, const char __user *buf,
> -- 
> 2.21.0
> 

--
Chuck Lever