Messages in this thread | | | Date | Tue, 19 Nov 2013 15:33:06 -0800 (PST) | From | Venkat Venkatsubra <> | Subject | RE: [PATCH] rds: Error on offset mismatch if not loopback |
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We now have lot more information than we did before. When sending a "congestion update" in rds_ib_xmit() we are now returning an incorrect number as bytes sent:
BUG_ON(off % RDS_FRAG_SIZE); BUG_ON(hdr_off != 0 && hdr_off != sizeof(struct rds_header));
/* 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); 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; }
It returns min(8240, 4096-0) i.e. 4096 bytes. The caller rds_send_xmit() is made to think a partial message (4096 out of 8240) was sent. It calls rds_ib_xmit() again with a data offset "off" of 4096-48 (rds header) (=4048 bytes). And we hit the BUG_ON.
The reason I didn't hit the panic on my test on Oracle UEK2 which is based on 2.6.39 kernel is it had it like this: BUG_ON(off % RDS_FRAG_SIZE); BUG_ON(hdr_off != 0 && hdr_off != sizeof(struct rds_header));
/* 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; } (So it wasn't 100% 2.6.39 ;-). ) It returned 8240 bytes. The caller rds_send_xmit decides the full message was sent (48 byte header + 4096 data + 4096 data). And it worked.
Then I found this info on the change that was done upstream which now causes the panic: http://marc.info/?l=linux-netdev&m=129908332903057 http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6094628bfd94323fc1cea05ec2c6affd98c18f7f
Will investigate more into which problem the above change addressed.
Venkat
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