[LU-12122] Deadlock with check_routers_before_use and discovery

• Type: Bug
• Resolution: Not a Bug
• Priority: Minor
• Affects Version/s: Lustre 2.12.0
• Severity: 3
• Assignee: WC Triage
• Reporter: Chris Horn

Description

I found this issue when testing Amir's new patches (see https://review.whamcloud.com/#/c/33651/9), but I believe the issue exists in current master.

LNetNIInit() calls lnet_monitor_thr_start() -> lnet_router_post_mt_start() -> lnet_wait_known_routerstate()

lnet_wait_known_routerstate() will wait indefinitely until all gateways have been discovered.

However, the discovery thread is not started until after lnet_monitor_thr_start() returns. Thus, LNet never finishes starting.

Logs slowly fill with:

[7073564.123980] LNetError: 31952:0:(router.c:873:lnet_check_routers()) Failed to discover router 192.168.2.26@tcp4

Reproduced on simple three node VM.

The LNet configuration:

sles15build01:/etc/modprobe.d # pdsh -w sles15build01,sles15c01,sles15s01 cat /etc/modprobe.d/lnet.conf | dshbak -c
----------------
sles15s01
----------------
options lnet networks="tcp(eth0)"
options lnet routes="tcp4 192.168.2.26@tcp"
options lnet lnet_peer_discovery_disabled=0
options lnet check_routers_before_use=1
----------------
sles15c01
----------------
options lnet ip2nets="tcp4(eth0) 192.168.*.*; tcp99(eth0) 192.168.*.*"
options lnet routes="tcp 192.168.2.26@tcp4"
options lnet lnet_peer_discovery_disabled=0
options lnet check_routers_before_use=1
----------------
sles15build01
----------------
options lnet ip2nets="tcp(eth0) 192.168.*.*; tcp4(eth1) 192.168.*.*; tcp99(eth1) 192.168.*.*"
options lnet forwarding=enabled
options lnet lnet_peer_discovery_disabled=0
sles15build01:/etc/modprobe.d #

Attempt to start LNet:

sles15build01:/etc/modprobe.d # pdsh -w sles15build01,sles15c01,sles15s01
pdsh> modprobe lnet
pdsh> lctl net up
sles15build01: LNET configured

LNet can start on the node acting as a router, but the hangs indefinitely on the other two nodes.