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Subject[PATCH 4.19 228/321] net/smc: fix sender_free computation
Date
From: Ursula Braun <ubraun@linux.ibm.com>

[ Upstream commit b8649efad879c69c7ab1f19ce8814fcabef1f72b ]

In some scenarios a separate consumer cursor update is necessary.
The decision is made in smc_tx_consumer_cursor_update(). The
sender_free computation could be wrong:

The rx confirmed cursor is always smaller than or equal to the
rx producer cursor. The parameters in the smc_curs_diff() call
have to be exchanged, otherwise sender_free might even be negative.

And if more data arrives local_rx_ctrl.prod might be updated, enabling
a cursor difference between local_rx_ctrl.prod and rx confirmed cursor
larger than the RMB size. This case is not covered by smc_curs_diff().
Thus function smc_curs_diff_large() is introduced here.

If a recvmsg() is processed in parallel, local_tx_ctrl.cons might
change during smc_cdc_msg_send. Make sure rx_curs_confirmed is updated
with the actually sent local_tx_ctrl.cons value.

Fixes: e82f2e31f559 ("net/smc: optimize consumer cursor updates")
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/smc/smc_cdc.c | 5 +++--
net/smc/smc_cdc.h | 26 +++++++++++++++++++++++++-
net/smc/smc_tx.c | 3 ++-
3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
index ed5dcf03fe0b6..8f691b5a44ddf 100644
--- a/net/smc/smc_cdc.c
+++ b/net/smc/smc_cdc.c
@@ -96,6 +96,7 @@ int smc_cdc_msg_send(struct smc_connection *conn,
struct smc_wr_buf *wr_buf,
struct smc_cdc_tx_pend *pend)
{
+ union smc_host_cursor cfed;
struct smc_link *link;
int rc;

@@ -107,10 +108,10 @@ int smc_cdc_msg_send(struct smc_connection *conn,
conn->local_tx_ctrl.seqno = conn->tx_cdc_seq;
smc_host_msg_to_cdc((struct smc_cdc_msg *)wr_buf,
&conn->local_tx_ctrl, conn);
+ smc_curs_copy(&cfed, &((struct smc_host_cdc_msg *)wr_buf)->cons, conn);
rc = smc_wr_tx_send(link, (struct smc_wr_tx_pend_priv *)pend);
if (!rc)
- smc_curs_copy(&conn->rx_curs_confirmed,
- &conn->local_tx_ctrl.cons, conn);
+ smc_curs_copy(&conn->rx_curs_confirmed, &cfed, conn);

return rc;
}
diff --git a/net/smc/smc_cdc.h b/net/smc/smc_cdc.h
index 934df4473a7ce..2377a51772d51 100644
--- a/net/smc/smc_cdc.h
+++ b/net/smc/smc_cdc.h
@@ -135,7 +135,9 @@ static inline void smc_curs_copy_net(union smc_cdc_cursor *tgt,
#endif
}

-/* calculate cursor difference between old and new, where old <= new */
+/* calculate cursor difference between old and new, where old <= new and
+ * difference cannot exceed size
+ */
static inline int smc_curs_diff(unsigned int size,
union smc_host_cursor *old,
union smc_host_cursor *new)
@@ -160,6 +162,28 @@ static inline int smc_curs_comp(unsigned int size,
return smc_curs_diff(size, old, new);
}

+/* calculate cursor difference between old and new, where old <= new and
+ * difference may exceed size
+ */
+static inline int smc_curs_diff_large(unsigned int size,
+ union smc_host_cursor *old,
+ union smc_host_cursor *new)
+{
+ if (old->wrap < new->wrap)
+ return min_t(int,
+ (size - old->count) + new->count +
+ (new->wrap - old->wrap - 1) * size,
+ size);
+
+ if (old->wrap > new->wrap) /* wrap has switched from 0xffff to 0x0000 */
+ return min_t(int,
+ (size - old->count) + new->count +
+ (new->wrap + 0xffff - old->wrap) * size,
+ size);
+
+ return max_t(int, 0, (new->count - old->count));
+}
+
static inline void smc_host_cursor_to_cdc(union smc_cdc_cursor *peer,
union smc_host_cursor *local,
struct smc_connection *conn)
diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index f1f621675db01..0ecbbdc337b82 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -595,7 +595,8 @@ void smc_tx_consumer_update(struct smc_connection *conn, bool force)
if (to_confirm > conn->rmbe_update_limit) {
smc_curs_copy(&prod, &conn->local_rx_ctrl.prod, conn);
sender_free = conn->rmb_desc->len -
- smc_curs_diff(conn->rmb_desc->len, &prod, &cfed);
+ smc_curs_diff_large(conn->rmb_desc->len,
+ &cfed, &prod);
}

if (conn->local_rx_ctrl.prod_flags.cons_curs_upd_req ||
--
2.20.1


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