Re: [PATCH for-rc] IB/rdmavt: Fix RQ counting issues causing use of an invalid RWQE

[Honggang LI <honli@redhat.com>]

On Tue, Jul 28, 2020 at 02:38:48PM -0400, Mike Marciniszyn wrote:
> The lookaside count is improperly initialized to the size of the
> Receive Queue with the additional +1.  In the traces below, the
> RQ size is 384, so the count was set to 385.
> 
> The lookaside count is then rarely refreshed.  Note the high and
> incorrect count in the trace below:
> 
> rvt_get_rwqe: [hfi1_0] wqe ffffc900078e9008 wr_id 55c7206d75a0 qpn c
> 	qpt 2 pid 3018 num_sge 1 head 1 tail 0, count 385
> rvt_get_rwqe: (hfi1_rc_rcv+0x4eb/0x1480 [hfi1] <- rvt_get_rwqe) ret=0x1
> 
> The head,tail indicate there is only one RWQE posted although the count
> says 385 and we correctly return the element 0.
> 
> The next call to rvt_get_rwqe with the decremented count:
> 
> rvt_get_rwqe: [hfi1_0] wqe ffffc900078e9058 wr_id 0 qpn c
> 	qpt 2 pid 3018 num_sge 0 head 1 tail 1, count 384
> rvt_get_rwqe: (hfi1_rc_rcv+0x4eb/0x1480 [hfi1] <- rvt_get_rwqe) ret=0x1
> 
> Note that the RQ is empty (head == tail) yet we return the RWQE at tail 1,
> which is not valid because of the bogus high count.
> 
> Best case, the RWQE has never been posted and the rc logic sees an RWQE
> that is too small (all zeros) and puts the QP into an error state.
> 
> In the worst case, a server slow at posting receive buffers might fool
> rvt_get_rwqe() into fetching an old RWQE and corrupt memory.
> 
> Fix by deleting the faulty initialization code and creating an
> inline to fetch the posted count and convert all callers to use
> new inline.
> 
> Fixes: f592ae3c999f ("IB/rdmavt: Fracture single lock used for posting and processing RWQEs")

Confirmed this patch works for me. Thanks

Tested-by: Honggang Li <honli@redhat.com>