Return-Path: Received: from mx143.netapp.com ([216.240.21.24]:37154 "EHLO mx143.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752824AbcCJRB5 (ORCPT ); Thu, 10 Mar 2016 12:01:57 -0500 Subject: Re: [PATCH v3 05/11] xprtrdma: Do not wait if ib_post_send() fails To: Chuck Lever , Sagi Grimberg References: <20160304162447.13590.9524.stgit@oracle120-ib.cthon.org> <20160304162801.13590.89343.stgit@oracle120-ib.cthon.org> <56DF1186.3030303@dev.mellanox.co.il> <8696EFBA-B7DB-42AC-AB57-C656070F4ED3@oracle.com> <56E00483.2060304@dev.mellanox.co.il> <6B59B087-9CFA-458B-8848-B08B8E14E2C7@oracle.com> <56E14BA2.2050504@dev.mellanox.co.il> <54ECE0AF-A930-45E0-A03A-FB7CD789B538@oracle.com> CC: Linux RDMA Mailing List , Linux NFS Mailing List From: Anna Schumaker Message-ID: <56E1A870.5030308@Netapp.com> Date: Thu, 10 Mar 2016 12:01:36 -0500 MIME-Version: 1.0 In-Reply-To: <54ECE0AF-A930-45E0-A03A-FB7CD789B538@oracle.com> Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: On 03/10/2016 11:40 AM, Chuck Lever wrote: > >> On Mar 10, 2016, at 5:25 AM, Sagi Grimberg wrote: >> >> >>>> Moving the QP into error state right after with rdma_disconnect >>>> you are not sure that none of the subset of the invalidations >>>> that _were_ posted completed and you get the corresponding MRs >>>> in a bogus state... >>> >>> Moving the QP to error state and then draining the CQs means >>> that all LOCAL_INV WRs that managed to get posted will get >>> completed or flushed. That's already handled today. >>> >>> It's the WRs that didn't get posted that I'm worried about >>> in this patch. >>> >>> Are there RDMA consumers in the kernel that use that third >>> argument to recover when LOCAL_INV WRs cannot be posted? >> >> None :) >> >>>>> I suppose I could reset these MRs instead (that is, >>>>> pass them to ib_dereg_mr). >>>> >>>> Or, just wait for a completion for those that were posted >>>> and then all the MRs are in a consistent state. >>> >>> When a LOCAL_INV completes with IB_WC_SUCCESS, the associated >>> MR is in a known state (ie, invalid). >>> >>> The WRs that flush mean the associated MRs are not in a known >>> state. Sometimes the MR state is different than the hardware >>> state, for example. Trying to do anything with one of these >>> inconsistent MRs results in IB_WC_BIND_MW_ERR until the thing >>> is deregistered. >> >> Correct. >> >>> The xprtrdma completion handlers mark the MR associated with >>> a flushed LOCAL_INV WR "stale". They all have to be reset with >>> ib_dereg_mr to guarantee they are usable again. Have a look at >>> __frwr_recovery_worker(). >> >> Yes, I'm aware of that. >> >>> And, xprtrdma waits for only the last LOCAL_INV in the chain to >>> complete. If that one isn't posted, then fr_done is never woken >>> up. In that case, frwr_op_unmap_sync() would wait forever. >> >> Ah.. so the (missing) completions is the problem, now I get >> it. >> >>> If I understand you I think the correct solution is for >>> frwr_op_unmap_sync() to regroup and reset the MRs associated >>> with the LOCAL_INV WRs that were never posted, using the same >>> mechanism as __frwr_recovery_worker() . >> >> Yea, I'd recycle all the MRs instead of having non-trivial logic >> to try and figure out MR states... > > We have to keep that logic, since a spurious disconnect > will result in flushed LOCAL_INV requests too. In fact > that's the by far more likely source of inconsistent MRs. > > >>> It's already 4.5-rc7, a little late for a significant rework >>> of this patch, so maybe I should drop it? >> >> Perhaps... Although you can make it incremental because the current >> patch doesn't seem to break anything, just not solving the complete >> problem... > > I'm preparing to extend the frwr_queue_recovery mechanism > in v4.7 to deal with other cases, and that new code could > be used here to fence MRs, rather than forcing a disconnect. > > I'd like to leave 05/11 in place for v4.6. > > Anna, can you add Sagi's Reviewed-by tags to the other > patches in this series, as he posted earlier this week? Yeah, I can do that. I'll leave in the patch, and send everything to Trond later this afternoon or tomorrow! Anna > > > -- > Chuck Lever > > >