Prior to
commit d021fabf52 ("rds: rdma: add consumer reject")
function "rds_rdma_cm_event_handler_cmn" would always honor a rejected
connection attempt by issuing a "rds_conn_drop".
The commit mentioned above added a "break", eliminating
the "fallthrough" case and made the "rds_conn_drop" rather conditional:
Now it only happens if a "consumer defined" reject (i.e. "rdma_reject")
carries an integer-value of "1" inside "private_data":
if (!conn)
break;
err = (int *)rdma_consumer_reject_data(cm_id, event, &len);
if (!err || (err && ((*err) == RDS_RDMA_REJ_INCOMPAT))) {
pr_warn("RDS/RDMA: conn <%pI6c, %pI6c> rejected, dropping connection\n",
&conn->c_laddr, &conn->c_faddr);
conn->c_proposed_version = RDS_PROTOCOL_COMPAT_VERSION;
rds_conn_drop(conn);
}
rdsdebug("Connection rejected: %s\n",
rdma_reject_msg(cm_id, event->status));
break;
/* FALLTHROUGH */
A number of issues are worth mentioning here:
#1) Previous versions of the RDS code simply rejected a connection
by calling "rdma_reject(cm_id, NULL, 0);"
So the value of the payload in "private_data" will not be "1",
but "0".
#2) Now the code has become dependent on host byte order and sizing.
If one peer is big-endian, the other is little-endian,
or there's a difference in sizeof(int) (e.g. ILP64 vs LP64),
the *err check does not work as intended.
#3) There is no check for "len" to see if the data behind *err is even valid.
Luckily, it appears that the "rdma_reject(cm_id, NULL, 0)" will always
carry 148 bytes of zeroized payload.
But that should probably not be relied upon here.
#4) With the added "break;",
we might as well drop the misleading "/* FALLTHROUGH */" comment.
This commit does _not_ address issue #2, as the sender would have to
agree on a byte order as well.
Here is the sequence of messages in this observed error-scenario:
Host-A is pre-QoS changes (excluding the commit mentioned above)
Host-B is post-QoS changes (including the commit mentioned above)
#1 Host-B
issues a connection request via function "rds_conn_path_transition"
connection state transitions to "RDS_CONN_CONNECTING"
#2 Host-A
rejects the incompatible connection request (from #1)
It does so by calling "rdma_reject(cm_id, NULL, 0);"
#3 Host-B
receives an "RDMA_CM_EVENT_REJECTED" event (from #2)
But since the code is changed in the way described above,
it won't drop the connection here, simply because "*err == 0".
#4 Host-A
issues a connection request
#5 Host-B
receives an "RDMA_CM_EVENT_CONNECT_REQUEST" event
and ends up calling "rds_ib_cm_handle_connect".
But since the state is already in "RDS_CONN_CONNECTING"
(as of #1) it will end up issuing a "rdma_reject" without
dropping the connection:
if (rds_conn_state(conn) == RDS_CONN_CONNECTING) {
/* Wait and see - our connect may still be succeeding */
rds_ib_stats_inc(s_ib_connect_raced);
}
goto out;
#6 Host-A
receives an "RDMA_CM_EVENT_REJECTED" event (from #5),
drops the connection and tries again (goto #4) until it gives up.
Tested-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
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