Merge branch 'for-next' of git://git.samba.org/sfrench/cifs-2.6

Pull CIFS fixes from Steve French:
 "Two minor cifs fixes and a minor documentation cleanup for cifs.txt"

* 'for-next' of git://git.samba.org/sfrench/cifs-2.6:
  cifs: update cifs.txt and remove some outdated infos
  cifs: Avoid calling unlock_page() twice in cifs_readpage() when using fscache
  cifs: Do not take a reference to the page in cifs_readpage_worker()

Documentation/filesystems/cifs/cifs.txt

   This is the client VFS module for the Common Internet File System
   (CIFS) protocol which is the successor to the Server Message Block 
   (SMB) protocol, the native file sharing mechanism for most early
-  PC operating systems.  CIFS is fully supported by current network
-  file servers such as Windows 2000, Windows 2003 (including  
-  Windows XP) as well by Samba (which provides excellent CIFS
+  PC operating systems. New and improved versions of CIFS are now
+  called SMB2 and SMB3. These dialects are also supported by the
+  CIFS VFS module. CIFS is fully supported by network
+  file servers such as Windows 2000, 2003, 2008 and 2012
+  as well by Samba (which provides excellent CIFS
   server support for Linux and many other operating systems), so
   this network filesystem client can mount to a wide variety of
-  servers.  The smbfs module should be used instead of this cifs module
-  for mounting to older SMB servers such as OS/2.  The smbfs and cifs
-  modules can coexist and do not conflict.  The CIFS VFS filesystem
-  module is designed to work well with servers that implement the
-  newer versions (dialects) of the SMB/CIFS protocol such as Samba, 
-  the program written by Andrew Tridgell that turns any Unix host 
-  into a SMB/CIFS file server.
+  servers.
 
   The intent of this module is to provide the most advanced network
   file system function for CIFS compliant servers, including better
@@ -24,28 +20,12 @@
   alternative to NFSv4 for fileserving in some Linux to Linux environments,
   not just in Linux to Windows environments.
 
-  This filesystem has an optional mount utility (mount.cifs) that can
-  be obtained from the project page and installed in the path in the same
-  directory with the other mount helpers (such as mount.smbfs). 
-  Mounting using the cifs filesystem without installing the mount helper
-  requires specifying the server's ip address.
+  This filesystem has an mount utility (mount.cifs) that can be obtained from
 
-  For Linux 2.4:
-    mount //anything/here /mnt_target -o
-            user=username,pass=password,unc=//ip_address_of_server/sharename
+      https://ftp.samba.org/pub/linux-cifs/cifs-utils/
 
-  For Linux 2.5: 
-    mount //ip_address_of_server/sharename /mnt_target -o user=username, pass=password
+  It must be installed in the directory with the other mount helpers.
 
+  For more information on the module see the project wiki page at
 
-  For more information on the module see the project page at
-
-      http://us1.samba.org/samba/Linux_CIFS_client.html 
-
-  For more information on CIFS see:
-
-      http://www.snia.org/tech_activities/CIFS
-
-  or the Samba site:
-     
-      http://www.samba.org
+      https://wiki.samba.org/index.php/LinuxCIFS_utils

fs/cifs/file.c

@@ -3379,6 +3379,9 @@ static int cifs_readpages(struct file *file, struct address_space *mapping,
 	return rc;
 }
 
+/*
+ * cifs_readpage_worker must be called with the page pinned
+ */
 static int cifs_readpage_worker(struct file *file, struct page *page,
 	loff_t *poffset)
 {
@@ -3390,7 +3393,6 @@ static int cifs_readpage_worker(struct file *file, struct page *page,
 	if (rc == 0)
 		goto read_complete;
 
-	page_cache_get(page);
 	read_data = kmap(page);
 	/* for reads over a certain size could initiate async read ahead */
 
@@ -3417,7 +3419,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page,
 
 io_error:
 	kunmap(page);
-	page_cache_release(page);
+	unlock_page(page);
 
 read_complete:
 	return rc;
@@ -3442,8 +3444,6 @@ static int cifs_readpage(struct file *file, struct page *page)
 
 	rc = cifs_readpage_worker(file, page, &offset);
 
-	unlock_page(page);
-
 	free_xid(xid);
 	return rc;
 }
@@ -3497,6 +3497,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
 			loff_t pos, unsigned len, unsigned flags,
 			struct page **pagep, void **fsdata)
 {
+	int oncethru = 0;
 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 	loff_t offset = pos & (PAGE_CACHE_SIZE - 1);
 	loff_t page_start = pos & PAGE_MASK;
@@ -3506,6 +3507,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
 
 	cifs_dbg(FYI, "write_begin from %lld len %d\n", (long long)pos, len);
 
+start:
 	page = grab_cache_page_write_begin(mapping, index, flags);
 	if (!page) {
 		rc = -ENOMEM;
@@ -3547,13 +3549,16 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
 		}
 	}
 
-	if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
+	if ((file->f_flags & O_ACCMODE) != O_WRONLY && !oncethru) {
 		/*
 		 * might as well read a page, it is fast enough. If we get
 		 * an error, we don't need to return it. cifs_write_end will
 		 * do a sync write instead since PG_uptodate isn't set.
 		 */
 		cifs_readpage_worker(file, page, &page_start);
+		page_cache_release(page);
+		oncethru = 1;
+		goto start;
 	} else {
 		/* we could try using another file handle if there is one -
 		   but how would we lock it to prevent close of that handle