[PATCH] IB/hfi1: Fix sdma.h tx->num_descs off-by-one error (take two)

[Daniel Vacek]

Unfortunately the commit `fd8958efe877` introduced another error
causing the `descs` array to overflow. This reults in further crashes
easily reproducible by `sendmsg` system call.

[ 1080.836473] general protection fault, probably for non-canonical address 0x400300015528b00a: 0000 [#1] PREEMPT SMP PTI
[ 1080.869326] RIP: 0010:hfi1_ipoib_build_ib_tx_headers.constprop.0+0xe1/0x2b0 [hfi1]
--
[ 1080.974535] Call Trace:
[ 1080.976990]  <TASK>
[ 1081.021929]  hfi1_ipoib_send_dma_common+0x7a/0x2e0 [hfi1]
[ 1081.027364]  hfi1_ipoib_send_dma_list+0x62/0x270 [hfi1]
[ 1081.032633]  hfi1_ipoib_send+0x112/0x300 [hfi1]
[ 1081.042001]  ipoib_start_xmit+0x2a9/0x2d0 [ib_ipoib]
[ 1081.046978]  dev_hard_start_xmit+0xc4/0x210
--
[ 1081.148347]  __sys_sendmsg+0x59/0xa0

crash> ipoib_txreq 0xffff9cfeba229f00
struct ipoib_txreq {
  txreq = {
    list = {
      next = 0xffff9cfeba229f00,
      prev = 0xffff9cfeba229f00
    },
    descp = 0xffff9cfeba229f40,
    coalesce_buf = 0x0,
    wait = 0xffff9cfea4e69a48,
    complete = 0xffffffffc0fe0760 <hfi1_ipoib_sdma_complete>,
    packet_len = 0x46d,
    tlen = 0x0,
    num_desc = 0x0,
    desc_limit = 0x6,
    next_descq_idx = 0x45c,
    coalesce_idx = 0x0,
    flags = 0x0,
    descs = {{
        qw = {0x8024000120dffb00, 0x4}  # SDMA_DESC0_FIRST_DESC_FLAG (bit 63)
      }, {
        qw = {  0x3800014231b108, 0x4}
      }, {
        qw = { 0x310000e4ee0fcf0, 0x8}
      }, {
        qw = {  0x3000012e9f8000, 0x8}
      }, {
        qw = {  0x59000dfb9d0000, 0x8}
      }, {
        qw = {  0x78000e02e40000, 0x8}
      }}
  },
  sdma_hdr =  0x400300015528b000,  <<< invalid pointer in the tx request structure
  sdma_status = 0x0,                   SDMA_DESC0_LAST_DESC_FLAG (bit 62)
  complete = 0x0,
  priv = 0x0,
  txq = 0xffff9cfea4e69880,
  skb = 0xffff9d099809f400
}

With this patch the crashes are no longer reproducible and the machine is stable.

Note, the header file changes are just an unrelated clean-up while I was looking
around trying to find the bug.

Fixes: fd8958efe877 ("IB/hfi1: Fix sdma.h tx->num_descs off-by-one errors")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Mats Kronberg <kronberg@xxxxxxxxxx>
Tested-by: Mats Kronberg <kronberg@xxxxxxxxxx>
Signed-off-by: Daniel Vacek <neelx@xxxxxxxxxx>
---
 drivers/infiniband/hw/hfi1/sdma.c |  2 +-
 drivers/infiniband/hw/hfi1/sdma.h | 17 +++++++----------
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/sdma.c b/drivers/infiniband/hw/hfi1/sdma.c
index 6e5ac2023328a..b67d23b1f2862 100644
--- a/drivers/infiniband/hw/hfi1/sdma.c
+++ b/drivers/infiniband/hw/hfi1/sdma.c
@@ -3158,7 +3158,7 @@ int _pad_sdma_tx_descs(struct hfi1_devdata *dd, struct sdma_txreq *tx)
 {
 	int rval = 0;
 
-	if ((unlikely(tx->num_desc + 1 == tx->desc_limit))) {
+	if ((unlikely(tx->num_desc == tx->desc_limit))) {
 		rval = _extend_sdma_tx_descs(dd, tx);
 		if (rval) {
 			__sdma_txclean(dd, tx);
diff --git a/drivers/infiniband/hw/hfi1/sdma.h b/drivers/infiniband/hw/hfi1/sdma.h
index d77246b48434f..362815a8da267 100644
--- a/drivers/infiniband/hw/hfi1/sdma.h
+++ b/drivers/infiniband/hw/hfi1/sdma.h
@@ -639,13 +639,13 @@ static inline void sdma_txclean(struct hfi1_devdata *dd, struct sdma_txreq *tx)
 static inline void _sdma_close_tx(struct hfi1_devdata *dd,
 				  struct sdma_txreq *tx)
 {
-	u16 last_desc = tx->num_desc - 1;
+	struct sdma_desc *desc = &tx->descp[tx->num_desc - 1];
 
-	tx->descp[last_desc].qw[0] |= SDMA_DESC0_LAST_DESC_FLAG;
-	tx->descp[last_desc].qw[1] |= dd->default_desc1;
+	desc->qw[0] |= SDMA_DESC0_LAST_DESC_FLAG;
+	desc->qw[1] |= dd->default_desc1;
 	if (tx->flags & SDMA_TXREQ_F_URGENT)
-		tx->descp[last_desc].qw[1] |= (SDMA_DESC1_HEAD_TO_HOST_FLAG |
-					       SDMA_DESC1_INT_REQ_FLAG);
+		desc->qw[1] |= (SDMA_DESC1_HEAD_TO_HOST_FLAG |
+				SDMA_DESC1_INT_REQ_FLAG);
 }
 
 static inline int _sdma_txadd_daddr(
@@ -670,13 +670,10 @@ static inline int _sdma_txadd_daddr(
 	tx->tlen -= len;
 	/* special cases for last */
 	if (!tx->tlen) {
-		if (tx->packet_len & (sizeof(u32) - 1)) {
+		if (tx->packet_len & (sizeof(u32) - 1))
 			rval = _pad_sdma_tx_descs(dd, tx);
-			if (rval)
-				return rval;
-		} else {
+		else
 			_sdma_close_tx(dd, tx);
-		}
 	}
 	return rval;
 }
-- 
2.43.0