[CIFS] Fix hang in find_writable_file

Caused by unneeded reopen during reconnect while spinlock held.

Fixes kernel bugzilla bug #7903

Thanks to Lin Feng Shen for testing this, and Amit Arora for
some nice problem determination to narrow this down.
Acked-by: Dave Kleikamp <shaggy@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/CHANGES

@@ -3,7 +3,10 @@ Version 1.50
 Fix NTLMv2 signing. NFS server mounted over cifs works (if cifs mount is
 done with "serverino" mount option).  Add support for POSIX Unlink
 (helps with certain sharing violation cases when server such as
-Samba supports newer POSIX CIFS Protocol Extensions).
+Samba supports newer POSIX CIFS Protocol Extensions). Add "nounix"
+mount option to allow disabling the CIFS Unix Extensions for just
+that mount. Fix hang on spinlock in find_writable_file (race when
+reopening file after session crash).
 
 Version 1.49
 ------------

fs/cifs/README

@@ -444,6 +444,13 @@ A partial list of the supported mount options follows:
  noposixpaths   If CIFS Unix extensions are supported, do not request
 		posix path name support (this may cause servers to
 		reject creatingfile with certain reserved characters).
+ nounix         Disable the CIFS Unix Extensions for this mount (tree
+		connection). This is rarely needed, but it may be useful
+		in order to turn off multiple settings all at once (ie
+		posix acls, posix locks, posix paths, symlink support
+		and retrieving uids/gids/mode from the server) or to
+		work around a bug in server which implement the Unix
+		Extensions.
  nobrl          Do not send byte range lock requests to the server.
 		This is necessary for certain applications that break
 		with cifs style mandatory byte range locks (and most

fs/cifs/TODO

@@ -82,8 +82,7 @@ u) DOS attrs - returned as pseudo-xattr in Samba format (check VFAT and NTFS for
 
 v) mount check for unmatched uids
 
-w) Add mount option for Linux extension disable per mount, and partial
-disable per mount (uid off, symlink/fifo/mknod on but what about posix acls?)
+w) Add support for new vfs entry points for setlease and fallocate 
 
 x) Fix Samba 3 server to handle Linux kernel aio so dbench with lots of 
 processes can proceed better in parallel (on the server)

fs/cifs/file.c

@@ -1904,6 +1904,25 @@ static int cifs_readpage(struct file *file, struct page *page)
 	return rc;
 }
 
+static int is_inode_writable(struct cifsInodeInfo *cifs_inode)
+{
+	struct cifsFileInfo *open_file;
+
+	read_lock(&GlobalSMBSeslock);
+	list_for_each_entry(open_file, &cifs_inode->openFileList, flist) {
+		if (open_file->closePend)
+			continue;
+		if (open_file->pfile &&
+		    ((open_file->pfile->f_flags & O_RDWR) ||
+		     (open_file->pfile->f_flags & O_WRONLY))) {
+			read_unlock(&GlobalSMBSeslock);
+			return 1;
+		}
+	}
+	read_unlock(&GlobalSMBSeslock);
+	return 0;
+}
+
 /* We do not want to update the file size from server for inodes
    open for write - to avoid races with writepage extending
    the file - in the future we could consider allowing
@@ -1912,19 +1931,13 @@ static int cifs_readpage(struct file *file, struct page *page)
    page caching in the current Linux kernel design */
 int is_size_safe_to_change(struct cifsInodeInfo *cifsInode, __u64 end_of_file)
 {
-	struct cifsFileInfo *open_file = NULL;
-
-	if (cifsInode)
-		open_file =  find_writable_file(cifsInode);
+	if (!cifsInode)
+		return 1;
 
-	if (open_file) {
+	if (is_inode_writable(cifsInode)) {
+		/* This inode is open for write at least once */
 		struct cifs_sb_info *cifs_sb;
 
-		/* there is not actually a write pending so let
-		this handle go free and allow it to
-		be closable if needed */
-		atomic_dec(&open_file->wrtPending);
-
 		cifs_sb = CIFS_SB(cifsInode->vfs_inode.i_sb);
 		if ( cifs_sb->mnt_cifs_flags & CIFS_MOUNT_DIRECT_IO ) {
 			/* since no page cache to corrupt on directio