On Tue, Aug 26, 2014 at 12:56 PM, Boaz Harrosh <boaz@xxxxxxxxxxxxx> wrote: > On 08/26/2014 06:36 PM, Trond Myklebust wrote: >> On Tue, Aug 26, 2014 at 11:24 AM, Matt W. Benjamin <matt@xxxxxxxxxxxx> wrote: >>> IIUC, the problem is the forechannel slot count, since the call you want to make synchronously is on the forechannel? > > > Matt no top post on a Linux mailing list ;-) > >> Yep. layoutcommit will be sent on the fore channel, which is why it >> can deadlock with the initial layoutget (or whatever operation that >> triggered the layout recall). > > Trond you said below: >> The above can deadlock if there are no session slots available to send >> the layoutcommit, in which case the recall won't complete, and the >> layoutget won't get a reply (which would free up the slot). > > Why would the layoutget not-get-a-reply ? > This is how it goes with Both ganesha server and knfsd last I tested. > > [1] > The LAYOUT_GET cause LAYOUT_RECALL case: (including the lo_commit) > > client Server comments > ~~~~~~ ~~~~~~ ~~~~~~~~ > LAYOUT_GET ==> > <== LAYOUT_GET_REPLAY(ERR_RECALL_CONFLICT) > <--------- fore-channel is free > <== RECALL > LAYOUT_COMMIT ==> > <== LAYOUT_COMMIT_REPLAY > <--------- fore-channel is free Beep! No free slots, so this hangs. > RECALL_REPLY(NO_MATCHING) => > <--------- back-channel is free > > Note that in this case the server is to send the RECALL only after > the error reply to LAYOUT_GET, specifically it is not aloud to get stuck > inside LAYOUT_GET and wait for the RECALL. (mandated by STD) > > [2] > The LAYOUT_GET sent all the while a RECALL is on the wire: > client Server comments > ~~~~~~ ~~~~~~ ~~~~~~~~ > <== RECALL > LAYOUT_GET ==> > <== LAYOUT_GET_REPLAY(ERR_RECALL_CONFLICT) > <--------- fore-channel is free > LAYOUT_COMMIT ==> > LAYOUT_COMMIT_REPLAY > <--------- fore-channel is free > RECALL_REPLY(NO_MATCHING) => > <--------- back-channel is free > > > [3] > Or the worst case that lo_commit needs to wait for the channel Similar > to [2] above: > > client Server comments > ~~~~~~ ~~~~~~ ~~~~~~~~ > <== RECALL > LAYOUT_GET ==> > initiate_lo_commit ==> slot is taken needs to wait > > <== LAYOUT_GET_REPLAY(ERR_RECALL_CONFLICT) > <--------- fore-channel is free > LAYOUT_COMMIT ==> slot is now free lo_commit goes through > <== LAYOUT_COMMIT_REPLAY > <--------- fore-channel is free > RECALL_REPLY(NO_MATCHING) => > <--------- back-channel is free > > So the most important is that the server must not get stuck in lo_get > and since there is a slot for each channel the lo_commit can be sent > from within the recall. > > What am I missing? > > Thanks > Boaz > -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@xxxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
