> 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? -- 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
