CIFS: Fix cache coherency for read oplock case

When we have a file opened with read oplock and we are writing a data
to this file, we need to store the data in the cache and then send to
the server to ensure that the next read operation will get a coherent
data.

Also mark it as CONFIG_CIFS_SMB2 because it's more suitable for SMB2
code but can fix some CIFS problems too (when server delays sending
an oplock break after a write request). We can drop this ifdefs
dependence in future.

Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 23 insertions, 4 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index ccad858d2d6..e93e3d2c69e 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2461,11 +2461,30 @@ cifs_strict_writev(struct kiocb *iocb, const struct iovec *iov,
                                                 iocb->ki_filp->private_data;
         struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
 
+#ifdef CONFIG_CIFS_SMB2
         /*
-         * In strict cache mode we need to write the data to the server exactly
-         * from the pos to pos+len-1 rather than flush all affected pages
-         * because it may cause a error with mandatory locks on these pages but
-         * not on the region from pos to ppos+len-1.
+         * If we have an oplock for read and want to write a data to the file
+         * we need to store it in the page cache and then push it to the server
+         * to be sure the next read will get a valid data.
+         */
+        if (!cinode->clientCanCacheAll && cinode->clientCanCacheRead) {
+                ssize_t written;
+                int rc;
+
+                written = generic_file_aio_write(iocb, iov, nr_segs, pos);
+                rc = filemap_fdatawrite(inode->i_mapping);
+                if (rc)
+                        return (ssize_t)rc;
+
+                return written;
+        }
+#endif
+
+        /*
+         * For non-oplocked files in strict cache mode we need to write the data
+         * to the server exactly from the pos to pos+len-1 rather than flush all
+         * affected pages because it may cause a error with mandatory locks on
+         * these pages but not on the region from pos to ppos+len-1.
          */
 
         if (!cinode->clientCanCacheAll)