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
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
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