[PATCH 3.16 079/305] RDMA/iw_cxgb4: Always wake up waiter in c4iw_peer_abort_intr()

Ben Hutchings
2016-08-14T11:53:54Z

From: Hariprasad S <hariprasad@chelsio.com>

commit 093108cb3640844cfdabb0f506fa6b592b64272d upstream.

Currently c4iw_peer_abort_intr() does not wake up the waiter if the
endpoint state indicates we're using MPAv2 and we're currently trying to
connect. This was introduced with commit 7c0a33d61187a ("RDMA/cxgb4:
Don't wakeup threads for MPAv2")

However, this original fix is flawed because it introduces a race that
can cause a deadlock of the iwarp stack. Here is the race:

->local side sets up an active offload connection.

->local side sends MPA_START request.

->peer sends MPA_START response.

->local side ingress cpl thread begins processing the MPA_START response,
but before it changes the state from MPA_REQ_SENT to FPDU_MODE:

->peer sends a RST which results in a ABORT_REQ_RSS. This triggers
peer_abort_intr() which sees the state in MPA_REQ_SENT and since mpa_rev
is 2, it will avoid waking up the endpoint with -ECONNRESET, assuming the
stack will re-attempt the connection using MPAv1.

->Meanwhile, the cpl thread moves the state to FPDU_MODE and calls
c4iw_modify_rc_qp() which calls rdma_init() which sends a RI_WR/INIT WR
to firmware. But since HW sent an abort, FW correctly drops the RI_WR/INIT
WR.

->So the cpl thread is stuck waiting for a reply and cannot process the
ABORT_REQ_RSS cpl sitting in its input queue. Thus everything comes to a
halt because no more ingress cpls are processed by the stack...

The correct fix for the issue is to always do the wake up in
c4iw_abort_intr() but reinitialize the wait object in c4iw_reconnect().

Fixes: 7c0a33d61187a ("RDMA/cxgb4: Don't wakeup threads for MPAv2")
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/infiniband/hw/cxgb4/cm.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)

--- a/drivers/infiniband/hw/cxgb4/cm.c
+++ b/drivers/infiniband/hw/cxgb4/cm.c
@@ -1904,6 +1904,7 @@ static int c4iw_reconnect(struct c4iw_ep

PDBG("%s qp %p cm_id %p\n", __func__, ep->com.qp, ep->com.cm_id);
init_timer(&ep->timer);
+ c4iw_init_wr_wait(&ep->com.wr_wait);

/*
* Allocate an active TID to initiate a TCP connection.
@@ -3875,16 +3876,7 @@ static int peer_abort_intr(struct c4iw_d
PDBG("%s ep %p tid %u state %u\n", __func__, ep, ep->hwtid,
ep->com.state);

- /*
- * Wake up any threads in rdma_init() or rdma_fini().
- * However, if we are on MPAv2 and want to retry with MPAv1
- * then, don't wake up yet.
- */
- if (mpa_rev == 2 && !ep->tried_with_mpa_v1) {
- if (ep->com.state != MPA_REQ_SENT)
- c4iw_wake_up(&ep->com.wr_wait, -ECONNRESET);
- } else
- c4iw_wake_up(&ep->com.wr_wait, -ECONNRESET);
+ c4iw_wake_up(&ep->com.wr_wait, -ECONNRESET);
sched(dev, skb);
return 0;
}