Hi, We run a Django / Celery application which makes heavy use of CIFS mounts. We are experiencing frequent reconnections / session startups and would like to understand how to avoid hammering the CIFS server and/or the authentication server. We've had multiple reports of DoS-like hammering from server admins, causing frequent re-authentication attempts and in one case causing core dumps on the CIFS server. Our CIFS client VMs have the following: OS: Ubuntu 18.04.3 Kernel: 4.15.0-58-generic mount.cifs: 6.8 Current mount options: rw,relatime,vers=3.0,sec=ntlmssp,cache=strict,soft,nounix,serverino,mapposix,rsize=1048576,wsize=1048576,echo_interval=60,actimeo=1 We don't run the CIFS server, but we can request any information required to diagnose the issue. Over the past 10 hours, one of our virtual machine's kernel log has accumulated: 8453 kern.log messages including "CIFS" To break that down, we have: 8305 "Free previous auth_key.response" messages 111 "validate protocol negotiate failed: -11" messages 26 "Close unmatched open" messages 7 "has not responded in 120 seconds" messages 4 "cifs_mount failed w/return code = -11" messages The server is an HSM (Hierarchical Storage Management) system, so it can be slow to respond if our application requests a file which is only available on tape, not on disk. The most common operation our application is performing on the CIFS-mounted files is calculating MD5 checksums - with many Celery worker processes running concurrently. We would appreciate any advice on how to investigate further. Thanks, James
