[PATCH v2] sunrpc: clean-up cache downcall

[PATCH v2] sunrpc: clean-up cache downcall

[Roberto Bergantinos Corpas]

We can simplify code around cache_downcall unifying memory
allocations using kvmalloc. This has the benefit of getting rid of
cache_slow_downcall (and queue_io_mutex), and also matches userland
allocation size and limits

Signed-off-by: Roberto Bergantinos Corpas <rbergant@redhat.com>
---
 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 20c93b68505e..1a2c1c44bb00 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -778,7 +778,6 @@ void cache_clean_deferred(void *owner)
  */
 
 static DEFINE_SPINLOCK(queue_lock);
-static DEFINE_MUTEX(queue_io_mutex);
 
 struct cache_queue {
 	struct list_head	list;
@@ -906,44 +905,26 @@ 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[32768]; /* 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

Re: [PATCH v2] sunrpc: clean-up cache downcall

[Chuck Lever]

> On Nov 27, 2020, at 1:38 PM, Roberto Bergantinos Corpas <rbergant@redhat.com> wrote:
> 
> We can simplify code around cache_downcall unifying memory
> allocations using kvmalloc. This has the benefit of getting rid of
> cache_slow_downcall (and queue_io_mutex), and also matches userland
> allocation size and limits
> 
> Signed-off-by: Roberto Bergantinos Corpas <rbergant@redhat.com>


Thanks, Roberto.

I see from linux-nfs history that Bruce explicitly asked for
this change, so applied for the next merge window. See the
cel-next topic branch in:

 git://git.linux-nfs.org/projects/cel/cel-2.6.git

or

 https://git.linux-nfs.org/?p=cel/cel-2.6.git;a=summary


> ---
> 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 20c93b68505e..1a2c1c44bb00 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -778,7 +778,6 @@ void cache_clean_deferred(void *owner)
>  */
> 
> static DEFINE_SPINLOCK(queue_lock);
> -static DEFINE_MUTEX(queue_io_mutex);
> 
> struct cache_queue {
> 	struct list_head	list;
> @@ -906,44 +905,26 @@ 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[32768]; /* 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