Kernel SRU request submitted:
https://lists.ubuntu.com/archives/kernel-team/2020-July/thread.html#111977
Updating status to 'In Progress'.
** Changed in: ubuntu-z-systems
Status: Triaged => In Progress
** Changed in: linux (Ubuntu Focal)
Status: Triaged => In Progress
** Changed in: linux (Ubuntu Groovy)
Status: Triaged => In Progress
** Description changed:
+ SRU Justification:
+ ==================
+
+ [Impact]
+
+ * Connections from later-level SMC (protocol) versions to an SMC-enabled
+ server on Linux hang.
+
+ * Later-level versions of SMC (although backwards-compatible) present a
+ higher version number and use larger messages during the CLC handshake.
+
+ * The solution to avoid such hangs is to introduce toleration for later
+ version numbers, and support CLC messages of arbitrary length.
+
+ [Fix]
+
+ * fb4f79264c0fc6fd5a68ffe3e31bfff97311e1f1 fb4f79264c0f "net/smc:
+ tolerate future SMCD versions"
+
+ [Test Case]
+
+ * Requires two IBM z13/z13s GA2 or LinuxONE Rockhopper/Emperor systems
+ with RoCE Express adapter v2(.1) for SMC-D usage.
+
+ * One system needs to run the initial SMC-D version, the other a newer
+ version.
+
+ * Establish a connection between both system and monitor/verify if it's
+ reliable or if it hangs.
+
+ [Regression Potential]
+
+ * The regression can be considered as medium to low:
+
+ * Since SMC-D is a pretty special way of doing shared memory
+ communications and not that wide-spread.
+
+ * However, the code that is changed is common code.
+
+ * But the patch is straight forward and only modifies /net/smc/smc_clc.c
+ and /net/smc/smc_clc.h
+
+ * It largely bumps limits (allows larger messages), adds a check and
+ introduces toleration, rather than changing control or flow.
+
+ [Other]
+
+ * The above fix is currently in 'linux-next' and tagged with
+ next-20200709.
+
+ * It is still assumed that it gets accepted for 5.8.
+
+ * However, since this is not guaranteed this SRU request is for focal
+ and groovy - to make sure that no potential regressions are introduced
+ in case the patch will not end up in 5.8.
+
+ __________
+
Description: smc: SMC connections hang with later-level implementations
Symptom: Connections from later-level SMC versions to an SMC-enabled
- server on Linux hang.
+ server on Linux hang.
Problem: Later-level versions of SMC present, although backwards-
- compatible, a higher version number, and use larger messages
- during the CLC handshake.
+ compatible, a higher version number, and use larger messages
+ during the CLC handshake.
Solution: Adjust for tolerating later version numbers, and support CLC
- messages of arbitrary length.
+ messages of arbitrary length.
Reproduction: Enable a server on Linux for SMC, and connect using a later-
- level version of SMC
+ level version of SMC
Applicable for: Ubuntu 20.04
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https://bugs.launchpad.net/bugs/1882088
Title:
[UBUNTU 20.04] smc: SMC connections hang with later-level
implementations
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