SUNRPC: Remove the global temporary write buffer in net/sunrpc/cache.c

While we do want to protect against multiple concurrent readers and writers
on each upcall/downcall pipe, we don't want to limit concurrent reading and
writing to separate caches.

This patch therefore replaces the static buffer 'write_buf', which can only
be used by one writer at a time, with use of the page cache as the
temporary buffer for downcalls. We still fall back to using the the old
global buffer if the downcall is larger than PAGE_CACHE_SIZE, since this is
apparently needed by the SPKM security context initialisation.

It then replaces the use of the global 'queue_io_mutex' with the
inode->i_mutex in cache_read() and cache_write().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 70 insertions, 25 deletions

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 062d4f4307e..c8e7d2d0726 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -27,6 +27,7 @@
 #include <linux/net.h>
 #include <linux/workqueue.h>
 #include <linux/mutex.h>
+#include <linux/pagemap.h>
 #include <asm/ioctls.h>
 #include <linux/sunrpc/types.h>
 #include <linux/sunrpc/cache.h>
@@ -702,13 +703,14 @@ cache_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
 {
         struct cache_reader *rp = filp->private_data;
         struct cache_request *rq;
-        struct cache_detail *cd = PDE(filp->f_path.dentry->d_inode)->data;
+        struct inode *inode = filp->f_path.dentry->d_inode;
+        struct cache_detail *cd = PDE(inode)->data;
         int err;
 
         if (count == 0)
                 return 0;
 
-        mutex_lock(&queue_io_mutex); /* protect against multiple concurrent
+        mutex_lock(&inode->i_mutex); /* protect against multiple concurrent
                               * readers on this file */
  again:
         spin_lock(&queue_lock);
@@ -721,7 +723,7 @@ cache_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
         }
         if (rp->q.list.next == &cd->queue) {
                 spin_unlock(&queue_lock);
-                mutex_unlock(&queue_io_mutex);
+                mutex_unlock(&inode->i_mutex);
                 BUG_ON(rp->offset);
                 return 0;
         }
@@ -768,38 +770,81 @@ cache_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
         }
         if (err == -EAGAIN)
                 goto again;
-        mutex_unlock(&queue_io_mutex);
+        mutex_unlock(&inode->i_mutex);
         return err ? err :  count;
 }
 
-static char write_buf[8192]; /* protected by queue_io_mutex */
+static ssize_t cache_do_downcall(char *kaddr, const char __user *buf,
+                                 size_t count, struct cache_detail *cd)
+{
+        ssize_t ret;
 
-static ssize_t
-cache_write(struct file *filp, const char __user *buf, size_t count,
-            loff_t *ppos)
+        if (copy_from_user(kaddr, buf, count))
+                return -EFAULT;
+        kaddr[count] = '\0';
+        ret = cd->cache_parse(cd, kaddr, count);
+        if (!ret)
+                ret = count;
+        return ret;
+}
+
+static ssize_t cache_slow_downcall(const char __user *buf,
+                                   size_t count, struct cache_detail *cd)
 {
-        int err;
-        struct cache_detail *cd = PDE(filp->f_path.dentry->d_inode)->data;
+        static char write_buf[8192]; /* protected by queue_io_mutex */
+        ssize_t ret = -EINVAL;
 
-        if (count == 0)
-                return 0;
         if (count >= sizeof(write_buf))
-                return -EINVAL;
-
+                goto out;
         mutex_lock(&queue_io_mutex);
+        ret = cache_do_downcall(write_buf, buf, count, cd);
+        mutex_unlock(&queue_io_mutex);
+out:
+        return ret;
+}
 
-        if (copy_from_user(write_buf, buf, count)) {
-                mutex_unlock(&queue_io_mutex);
-                return -EFAULT;
-        }
-        write_buf[count] = '\0';
-        if (cd->cache_parse)
-                err = cd->cache_parse(cd, write_buf, count);
-        else
-                err = -EINVAL;
+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;
+        ssize_t ret = -ENOMEM;
+
+        if (count >= PAGE_CACHE_SIZE)
+                goto out_slow;
+
+        page = find_or_create_page(mapping, 0, GFP_KERNEL);
+        if (!page)
+                goto out_slow;
+
+        kaddr = kmap(page);
+        ret = cache_do_downcall(kaddr, buf, count, cd);
+        kunmap(page);
+        unlock_page(page);
+        page_cache_release(page);
+        return ret;
+out_slow:
+        return cache_slow_downcall(buf, count, cd);
+}
 
-        mutex_unlock(&queue_io_mutex);
-        return err ? err : count;
+static ssize_t
+cache_write(struct file *filp, const char __user *buf, size_t count,
+            loff_t *ppos)
+{
+        struct address_space *mapping = filp->f_mapping;
+        struct inode *inode = filp->f_path.dentry->d_inode;
+        struct cache_detail *cd = PDE(inode)->data;
+        ssize_t ret = -EINVAL;
+
+        if (!cd->cache_parse)
+                goto out;
+
+        mutex_lock(&inode->i_mutex);
+        ret = cache_downcall(mapping, buf, count, cd);
+        mutex_unlock(&inode->i_mutex);
+out:
+        return ret;
 }
 
 static DECLARE_WAIT_QUEUE_HEAD(queue_wait);