From: David Laight <david.lai...@aculab.com> Date: Thu, 30 Apr 2015 15:23:39 +0000
> From: David Ahern >> Sent: 30 April 2015 15:28 >> rdma_conn_param private data is copied using memcpy after headers such >> as cma_hdr (see cma_resolve_ib_udp as example). so the start of the >> private data is aligned to the end of the structure that come before. if >> this structure end with u32 the meaning is that the start of the private >> data will be 4 bytes aligned. structures that use u8/u16/u32/u64 are >> naturally aligned but in case the structure start is not 8 bytes aligned, >> all u64 members of this structure will not be aligned. to solve this issue >> we must use special macros that allow unaligned access to those >> unaligned members. >> >> Addresses the following kernel log seen when attempting to use RDMA: >> >> Kernel unaligned access at TPC[10507a88] >> rds_ib_cm_connect_complete+0x1bc/0x1e0 [rds_rdma] > ... >> diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c >> index 31b74f5..e0bbbac 100644 >> --- a/net/rds/ib_cm.c >> +++ b/net/rds/ib_cm.c >> @@ -183,8 +183,17 @@ void rds_ib_cm_connect_complete(struct rds_connection >> *conn, struct rdma_cm_even >> >> /* If the peer gave us the last packet it saw, process this as if >> * we had received a regular ACK. */ >> - if (dp && dp->dp_ack_seq) >> - rds_send_drop_acked(conn, be64_to_cpu(dp->dp_ack_seq), NULL); > > Or just mark 'dp_ack_seq' with __attribute((aligned(4))). > Then the compiler will generate two 32bit loads. > (provided be64_to_cpu() doesn't do anything stupid.) It's a __be64 which already requires 8 byte alignment. That's not what is causing the problem here. It's the opaque area that this structure can end up being placed afterwards. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
