cifs: have find_writeable_file prefer filehandles opened by same task

When the CIFS client goes to write out pages, it needs to pick a
filehandle to write to. find_writeable_file however just picks the
first filehandle that it finds. This can cause problems when a lock
is issued against a particular filehandle and we pick a different
filehandle to write to.

This patch tries to avert this situation by having find_writable_file
prefer filehandles that have a pid that matches the current task.
This seems to fix lock test 11 from the connectathon test suite when
run against a windows server.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index cbefe1f1f9fe..d39e852a28a9 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1065,6 +1065,7 @@ struct cifsFileInfo *find_readable_file(struct cifsInodeInfo *cifs_inode)
 struct cifsFileInfo *find_writable_file(struct cifsInodeInfo *cifs_inode)
 {
         struct cifsFileInfo *open_file;
+        bool any_available = false;
         int rc;
 
         /* Having a null inode here (because mapping->host was set to zero by
@@ -1080,8 +1081,10 @@ struct cifsFileInfo *find_writable_file(struct cifsInodeInfo *cifs_inode)
         read_lock(&GlobalSMBSeslock);
 refind_writable:
         list_for_each_entry(open_file, &cifs_inode->openFileList, flist) {
-                if (open_file->closePend)
+                if (open_file->closePend ||
+                    (!any_available && open_file->pid != current->tgid))
                         continue;
+
                 if (open_file->pfile &&
                     ((open_file->pfile->f_flags & O_RDWR) ||
                      (open_file->pfile->f_flags & O_WRONLY))) {
@@ -1131,6 +1134,11 @@ refind_writable:
                            of the loop here. */
                 }
         }
+        /* couldn't find useable FH with same pid, try any available */
+        if (!any_available) {
+                any_available = true;
+                goto refind_writable;
+        }
         read_unlock(&GlobalSMBSeslock);
         return NULL;
 }