[PATCH] rds: prevent BUG_ON triggered on congestion update to loopback

[Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>]

From: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>

After congestion update on a local connection, when rds_ib_xmit returns
less bytes than that are there in the message, rds_send_xmit calls
back rds_ib_xmit with an offset that causes BUG_ON(off & RDS_FRAG_SIZE)
to trigger.

Reported-by: Josh Hunt <joshhunt00@gmail.com>
Tested-by: Honggang Li <honli@redhat.com>
Acked-by: Bang Nguyen <bang.nguyen@oracle.com>
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 net/rds/ib_send.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/rds/ib_send.c b/net/rds/ib_send.c
index e590949..37be6e2 100644
--- a/net/rds/ib_send.c
+++ b/net/rds/ib_send.c
@@ -552,9 +552,8 @@ int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
 	    && rm->m_inc.i_hdr.h_flags & RDS_FLAG_CONG_BITMAP) {
 		rds_cong_map_updated(conn->c_fcong, ~(u64) 0);
 		scat = &rm->data.op_sg[sg];
-		ret = sizeof(struct rds_header) + RDS_CONG_MAP_BYTES;
-		ret = min_t(int, ret, scat->length - conn->c_xmit_data_off);
-		return ret;
+		ret = max_t(int, RDS_CONG_MAP_BYTES, scat->length);
+		return sizeof(struct rds_header) + ret;
 	}
 
 	/* FIXME we may overallocate here */
-- 
1.7.6