Commit 093108cb authored May 06, 2016 by Hariprasad S Committed by Doug Ledford May 13, 2016

RDMA/iw_cxgb4: Always wake up waiter in c4iw_peer_abort_intr()



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 7c0a33d6 ("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: 7c0a33d6 ("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>

parent 4a4dd8db

drivers/infiniband/hw/cxgb4/cm.c

+2 −10

Original line number	Diff line number	Diff line
		@@ -2136,6 +2136,7 @@ static int c4iw_reconnect(struct c4iw_ep *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.
		@@ -4239,15 +4240,6 @@ static int peer_abort_intr(struct c4iw_dev dev, struct sk_buff skb)
		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);
		out:
		sched(dev, skb);