On 03/10/2016 11:40 AM, Chuck Lever wrote: > >> On Mar 10, 2016, at 5:25 AM, Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx> 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 > > > -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
