[LU-18172] server umount and lctl lfsck_stop race

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.17.0
• Severity: 3
• Assignee: Vladimir Saveliev
• Reporter: Vladimir Saveliev

Description

The following race between umount and lctl lfsck_stop has been observed:
lctl lfsck_stop is running..
umount start:

server_put_super
  class_manual_cleanup
    obd_precleanup
      mdt_device_fini
        mdt_fini
          mdd_iocontrol(OBD_IOC_STOP_LFSCK)
            lfsck_stop
              if (thread_is_stopping(thread))
                GOTO(unlock, rc = -EINPROGRESS);  <<< umount continues as lctl lfsck_stop has setup already SVC_STOPPING flag.

          /* various *fini()-s */
          mdt_fld_fini
            ss->ss_server_fld = NULL;

          mdt_stack_fini
            mdd_process_config
              lod_process_config
                osd_process_config(LCFG_CLEANUP)
                  osd_shutdown
                    osd_scrub_cleanup
                      LASSERT(dev->od_otable_it == NULL);   <<< hit this assertion as lfsck_master_engine() did not run osd_otable_it_fini() yet.

There was also seen another consequence of the problem:
lfsck failed at:

   lfsck_find_mdt_idx_by_fid
       rc = fld_server_lookup(env, ss->ss_server_fld...
         BUG: unable to handle kernel NULL pointer dereference

because ss->ss_server_fld is set to NULL in mdt_fld_fini() by umount. See above umount call trace.