SetDefaultProvider.java creates directories and files named m.jar or m.properties. These files are not cleaned up later.

  [...]
    94 Path patchdir = Files.createTempDirectory("patch");
  [...]
   108 Path patchdir = Files.createTempDirectory("patch");
  [...]
   145 Path jar = Files.createTempDirectory("tmp").resolve("m.jar");

The preferred approach would be to create temporary test directories and files under the jtreg property user.dir instead, if it is defined. During a jtreg run, user.dir has the value $PWD/JTwork/scratch