[Ocfs2-devel] May be deadlock for wrong locking order, patch request reviewed, thanks

[Guozhonghua]

As we test the ocfs2 cluster, the cluster is sometime hangs up.

I got some information about the dead lock, which cause the cluster hangs up, the sys dir / lock is held and the node did not release it which cause the cluster hangs up.
    root at cvknode-21:~# ps -e -o pid,stat,comm,wchan=WIDE-WCHAN-COLUMN | grep D
      PID STAT COMMAND WIDE-WCHAN-COLUMN
     7489 D jbd2/sdh-621 jbd2_journal_commit_transaction
    16218 D ls iterate_dir
    16533 D mkdir dlm_wait_for_lock_mastery
    31195 D+ ls iterate_dir

So the code reviewed, and I found the order of the lock may wrong.
In the function dlm_master_request_handler, the resource lock is held and so after the lock of &dlm->master_lock is locked.
But in the function dlm_get_lock_resource, the &dlm->master_lock is locked first and so resource lock.
They are different order in different function.
If there are two task, one holds the res->lock waiting for the dlm->master_lock, with the function dlm_master_request_handler.
Another task holds the &dlm->master_lock waiting for the res->lock with dlm_get_lock_resource.
So the deadlock may be up.

I changed some code, and the patch request reviews.



*** ocfs2-ko-3.16/dlm/dlmmaster.c      2014-09-11 12:45:45.821657634 +0800
--- ocfs2-ko-3.16_compared/dlm/dlmmaster.c      2014-09-11 18:54:34.970243238 +0800
*************** way_up_top:
*** 1506,1512 ****
--- 1506,1515 ----
              }

              // mlog(0, "lockres is in progress...\n");
+             spin_unlock(&res->spinlock);
+
              spin_lock(&dlm->master_lock);
+             spin_lock(&res->spinlock);
              found = dlm_find_mle(dlm, &tmpmle, name, namelen);
              if (!found) {
                      mlog(ML_ERROR, "no mle found for this lock!\n");
*************** way_up_top:
*** 1551,1558 ****
                      set_bit(request->node_idx, tmpmle->maybe_map);
              spin_unlock(&tmpmle->spinlock);

-              spin_unlock(&dlm->master_lock);
              spin_unlock(&res->spinlock);
+             spin_unlock(&dlm->master_lock);

              /* keep the mle attached to heartbeat events */
              dlm_put_mle(tmpmle);
-------------------------------------------------------------------------------------------------------------------------------------
????????????????????????????????????????
????????????????????????????????????????
????????????????????????????????????????
???
This e-mail and its attachments contain confidential information from H3C, which is
intended only for the person or entity whose address is listed above. Any use of the
information contained herein in any way (including, but not limited to, total or partial
disclosure, reproduction, or dissemination) by persons other than the intended
recipient(s) is prohibited. If you receive this e-mail in error, please notify the sender
by phone or email immediately and delete it!
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://oss.oracle.com/pipermail/ocfs2-devel/attachments/20140911/2a124d44/attachment-0001.html