If some exception is thrown while uploading file (for example, file size limit exceeded), then file deleted, but file channel is not closed. Linux lsof command shown a growing number of descriptors. I solved this problem by modifying io.undertow.server.handlers.form.MultiPartParserDefinition$MultiPartUploadHandler.parseBlocking()
exchange.putAttachment(FORM_DATA, data);
} catch (IOException e) {
try {
if (fileChannel != null)

} catch (Throwable ignored) {
}
throw e;
}
Added fileChannel.close(). May be, this code need to be moved in MultiPartUploadHandler.close()