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authorVenkat Venkatsubra <venkat.x.venkatsubra@oracle.com>2013-12-02 15:41:39 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-01-15 15:28:45 -0800
commitbb309e485a2c7e5c354ed0c3ed24a0714643e6bd (patch)
treefa4af86076f0c3114e8a99d5c7bfe196605ca611 /net
parent908e2eb543cf0c2e88d93cfd1ce9b83b2e951aa5 (diff)
downloadlinaro-lsk-bb309e485a2c7e5c354ed0c3ed24a0714643e6bd.tar.gz
rds: prevent BUG_ON triggered on congestion update to loopback
[ Upstream commit 18fc25c94eadc52a42c025125af24657a93638c0 ] 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. For a 4Kb PAGE_SIZE rds_ib_xmit returns min(8240,4096)=4096 when actually the message contains 8240 bytes. rds_send_xmit thinks there is more to send and calls rds_ib_xmit again with a data offset "off" of 4096-48(rds header) =4048 bytes thus hitting the BUG_ON(off & RDS_FRAG_SIZE) [RDS_FRAG_SIZE=4k]. The commit 6094628bfd94323fc1cea05ec2c6affd98c18f7f "rds: prevent BUG_ON triggering on congestion map updates" introduced this regression. That change was addressing the triggering of a different BUG_ON in rds_send_xmit() on PowerPC architecture with 64Kbytes PAGE_SIZE: BUG_ON(ret != 0 && conn->c_xmit_sg == rm->data.op_nents); This was the sequence it was going through: (rds_ib_xmit) /* Do not send cong updates to IB loopback */ if (conn->c_loopback && rm->m_inc.i_hdr.h_flags & RDS_FLAG_CONG_BITMAP) { rds_cong_map_updated(conn->c_fcong, ~(u64) 0); return sizeof(struct rds_header) + RDS_CONG_MAP_BYTES; } rds_ib_xmit returns 8240 rds_send_xmit: c_xmit_data_off = 0 + 8240 - 48 (rds header accounted only the first time) = 8192 c_xmit_data_off < 65536 (sg->length), so calls rds_ib_xmit again rds_ib_xmit returns 8240 rds_send_xmit: c_xmit_data_off = 8192 + 8240 = 16432, calls rds_ib_xmit again and so on (c_xmit_data_off 24672,32912,41152,49392,57632) rds_ib_xmit returns 8240 On this iteration this sequence causes the BUG_ON in rds_send_xmit: while (ret) { tmp = min_t(int, ret, sg->length - conn->c_xmit_data_off); [tmp = 65536 - 57632 = 7904] conn->c_xmit_data_off += tmp; [c_xmit_data_off = 57632 + 7904 = 65536] ret -= tmp; [ret = 8240 - 7904 = 336] if (conn->c_xmit_data_off == sg->length) { conn->c_xmit_data_off = 0; sg++; conn->c_xmit_sg++; BUG_ON(ret != 0 && conn->c_xmit_sg == rm->data.op_nents); [c_xmit_sg = 1, rm->data.op_nents = 1] What the current fix does: Since the congestion update over loopback is not actually transmitted as a message, all that rds_ib_xmit needs to do is let the caller think the full message has been transmitted and not return partial bytes. It will return 8240 (RDS_CONG_MAP_BYTES+48) when PAGE_SIZE is 4Kb. And 64Kb+48 when page size is 64Kb. 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: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net')
-rw-r--r--net/rds/ib_send.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/net/rds/ib_send.c b/net/rds/ib_send.c
index e5909498117..37be6e226d1 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 */