On Wed, Nov 09, 2016 at 12:33:35PM -0500, Jeff Layton wrote: > On Wed, 2016-11-09 at 11:27 -0500, J. Bruce Fields wrote: > > On Wed, Nov 09, 2016 at 08:18:08AM -0500, Jeff Layton wrote: > > > > > > On Tue, 2016-11-08 at 20:27 -0500, J. Bruce Fields wrote: > > > > > > > > On Tue, Nov 08, 2016 at 05:52:21PM -0500, Tejun Heo wrote: > > > > > > > > > > > > > > > Hello, Bruce. > > > > > > > > > > On Tue, Nov 08, 2016 at 04:39:11PM -0500, J. Bruce Fields wrote: > > > > > > > > > > > > > > > > > > Apologies, just cleaning out old mail and finding some I should have > > > > > > responded to long ago: > > > > > > > > > > > > On Wed, Aug 31, 2016 at 02:23:48AM +0530, Bhaktipriya Shridhar > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > The workqueue "callback_wq" queues a single work item > > > > > > > &cb->cb_work per > > > > > > > nfsd4_callback instance and thus, it doesn't require execution > > > > > > > ordering. > > > > > > > > > > > > What's "execution ordering"? > > > > > > > > > > > > AIUI, it means that jobs are always run in the order queued and are > > > serialized. > > > > > > > > > > > > > > > > > > > > > > > > We definitely do depend on the fact that at most one of these is > > > > > > running > > > > > > at a time. > > > > > > > > > > > We do? > > > > > > > > > > > > > > > > > If there can be multiple cb's and thus cb->cb_work's per callback_wq, > > > > > it'd need explicit ordering. Is that the case? > > > > > > > > > > These are basically client RPC tasks, and the cb_work just handles the > > > submission into the client RPC state machine. Just because we're running > > > several callbacks at the same time doesn't mean that they need to be > > > strictly ordered. The client state machine can certainly handle running > > > these in parallel. > > > > I'm not worried about the rpc calls themselves, I'm worried about the > > other stuff in nfsd4_run_cb_work(), especially > > nfsd4_process_cb_update(). > > > > It's been a while since I thought about it and maybe it'd be OK with a > > little bit of extra locking. > > > > --b. > > > > Ahh good point there. nfsd4_process_cb_update is a bit of a special > case, and I hadn't considered that. > > I think we could use the cl_lock to protect most of the fields that are > affected there. > > I'm not sure how to handle setup_callback_client though. Should we > serialize those calls so that we're only constructing one at a time and > have other threads wait on it? We could use a cl_flags bit for a > NFSD4_CLIENT_CB_CONSTRUCTING flag and serialize on those?
For now I wish we could just like to continue assuming the workqueue processes only one item at a time. Do we have that now, or do we need to switch to (looking at workqueue.h...) alloc_ordered workqueue()? --b.
