Red Hat Bugzilla – Bug 201015
GFS2 readdir - NFS interface
Last modified: 2007-11-30 17:07:32 EST
There are two interrlated problems here: 1. We have a different readdir path for NFS compared with "normal" readdir due to different locking requirements. The NFS path is slower. This might need to be resolved at the NFS end rather than the GFS end, but I'm making this a GFS2 bug for now until that can be looked at in more detail. Ken Preslan described the reasons for having the different code for NFS in the document he wrote just before he left. 2. We use the name of the current process as a way to switch between the NFS and "normal" readdir behaviour. This is certainly wrong. At the very least we might be able to use __builtin_return_address(0) for this since we only have a single code path which needs the NFS behaviour.
Created attachment 135534 [details] Message from Jan Engelhardt The message I've just attached contains a suggestion for making a change to the selection of the NFS path vs the "normal" path. It is a much better test than the current one of guessing according to the name of the process. Long term of course, we still want to eliminate the second code path completely, but thats a rather more long and involved job.
I've now removed the "NFS only" path from readdir. Having looked at this in a bit more detail, I'm not so sure that the deadlock can actually occur anyway. I have a feeling that the situation mentioned in the notes which Ken Preslan left us is not relevant any more since we lock directories before their content anyway now, and use the old "must lock in order" rule to break deadlocks at the directory level (in rename) first and again when locking the inodes at the next level down. I don't think we ever lock more than two levels at a time. Rename seems the only likely thing that we might deadlock against and I think we are safe there.
I think we can close this one now.