cifs: destage any unwritten data to the server before calling copychunk_write

because the copychunk_write might cover a region of the file that has not yet
been sent to the server and thus fail.

A simple way to reproduce this is:
truncate -s 0 /mnt/testfile; strace -f -o x -ttT xfs_io -i -f -c 'pwrite 0k 128k' -c 'fcollapse 16k 24k' /mnt/testfile

the issue is that the 'pwrite 0k 128k' becomes rearranged on the wire with
the 'fcollapse 16k 24k' due to write-back caching.

fcollapse is implemented in cifs.ko as a SMB2 IOCTL(COPYCHUNK_WRITE) call
and it will fail serverside since the file is still 0b in size serverside
until the writes have been destaged.
To avoid this we must ensure that we destage any unwritten data to the
server before calling COPYCHUNK_WRITE.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1997373
Reported-by: Xiaoli Feng <xifeng@redhat.com>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index a67df8eaf7026186b6e9efa0413731ff3ae4d167..d6aaeff4a30a530864211b79fbda744b87d6b720 100644 (file)
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1858,9 +1858,17 @@ smb2_copychunk_range(const unsigned int xid,
        int chunks_copied = 0;
        bool chunk_sizes_updated = false;
        ssize_t bytes_written, total_bytes_written = 0;
+       struct inode *inode;
 
        pcchunk = kmalloc(sizeof(struct copychunk_ioctl), GFP_KERNEL);
 
+       /*
+        * We need to flush all unwritten data before we can send the
+        * copychunk ioctl to the server.
+        */
+       inode = d_inode(trgtfile->dentry);
+       filemap_write_and_wait(inode->i_mapping);
+
        if (pcchunk == NULL)
                return -ENOMEM;