cifs/smb3: Fix data inconsistent when zero file range

CIFS implements the fallocate(FALLOC_FL_ZERO_RANGE) with send SMB
ioctl(FSCTL_SET_ZERO_DATA) to server. It just set the range of the
remote file to zero, but local page cache not update, then the data
inconsistent with server, which leads the xfstest generic/008 failed.

So we need to remove the local page caches before send SMB
ioctl(FSCTL_SET_ZERO_DATA) to server. After next read, it will
re-cache it.

Fixes: 30175628bf ("[SMB3] Enable fallocate -z support for SMB3 mounts")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Cc: stable@vger.kernel.org # v3.17
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -3188,6 +3188,11 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 	trace_smb3_zero_enter(xid, cfile->fid.persistent_fid, tcon->tid,
 			      ses->Suid, offset, len);
 
+	/*
+	 * We zero the range through ioctl, so we need remove the page caches
+	 * first, otherwise the data may be inconsistent with the server.
+	 */
+	truncate_pagecache_range(inode, offset, offset + len - 1);
 
 	/* if file not oplocked can't be sure whether asking to extend size */
 	if (!CIFS_CACHE_READ(cifsi))