[LU-16283] o2iblnd.c:3049:kiblnd_shutdown() <NID>: waiting for <N> peers to disconnect

• Type: Bug
• Resolution: Unresolved
• Priority: Minor
• Affects Version/s: Lustre 2.15.1
• Environment: 4.18.0-372.32.1.1toss.t4.x86_64 ; lustre-2.15.1_7.llnl-2.t4.x86_64
• Severity: 3
• Assignee: Serguei Smirnov
• Reporter: Olaf Faaland

Description

Observed on a lustre router node, while the servers and some of the clients were up and connected. The luster router node has Omnipath on the client side and IB on the lustre server side.

lnetctl lnet unconfigure 

hangs with stack

[<0>] kiblnd_shutdown+0x347/0x4e0 [ko2iblnd]
[<0>] lnet_shutdown_lndni+0x2b6/0x4c0 [lnet]
[<0>] lnet_shutdown_lndnet+0x6c/0xb0 [lnet]
[<0>] lnet_shutdown_lndnets+0x11e/0x300 [lnet]
[<0>] LNetNIFini+0xb7/0x130 [lnet]
[<0>] lnet_ioctl+0x220/0x260 [lnet]
[<0>] notifier_call_chain+0x47/0x70
[<0>] blocking_notifier_call_chain+0x42/0x60
[<0>] libcfs_psdev_ioctl+0x346/0x590 [libcfs]
[<0>] do_vfs_ioctl+0xa5/0x740
[<0>] ksys_ioctl+0x64/0xa0
[<0>] __x64_sys_ioctl+0x16/0x20
[<0>] do_syscall_64+0x5b/0x1b0
[<0>] entry_SYSCALL_64_after_hwframe+0x61/0xc6 

Debug log shows it's waiting for 3 peers, even after 3700 seconds:

00000800:00000200:1.0:1667256015.359743:0:35023:0:(o2iblnd.c:3049:kiblnd_shutdown()) 172.19.1.108@o2ib100: waiting for 3 peers to disconnect 
...
00000800:00000200:3.0:1667259799.039743:0:35023:0:(o2iblnd.c:3049:kiblnd_shutdown()) 172.19.1.108@o2ib100: waiting for 3 peers to disconnect

Before the shutdown there were 38 peers, all reported as "up"

For patch stack, see https://github.com/LLNL/lustre/releases/tag/2.15.1_7.llnl

For my reference, my local ticket is TOSS5826

Issue Links

• is related to: LU-17480 lustre_rmmod hangs if a lnet route is down

Comments

[Olaf Faaland]

This workaround seems to be working well for us. We do not bring NIs up and down dynamically in production normally, so the potential problem scenario probably won't occur and thus won't hurt us. So I'll remove topllnl, but leave the ticket open until an actual fix is identified.

[Serguei Smirnov]

Hi Olaf,

I haven't been able to conclusively identify the problem yet. I believe it has to do with some sort of race on LNet shutdown, but this is kind of obvious. The workaround you applied should be good for most cases, the only scenario it doesn't cover is probably when active router NI's are being brought down/up dynamically. 

Thanks,

Serguei.

[Olaf Faaland]

Hi Serguei,
I've added "lnetctl set routing 0" to our lnet service file. Have you had any success identifying the problem? Thanks

[Olaf Faaland]

Yes, we are adding "lnetctl set routing 0" to the shutdown tasks in our lnet service file after the holiday break.

[Serguei Smirnov]

Hi Olaf,

Sorry, not yet. It is not addressing the root cause, but, for the lack of better ideas, I was considering changing the shutdown procedure to include "lnetctl set routing 0", but haven't submitted the patch yet.

Thanks,

Serguei.

[Olaf Faaland]

Hi Serguei,

Do you have any update on this issue?

Thanks

[Olaf Faaland]

> I experimented with executing "lnetctl set routing 0" on the router node

Good idea.   Doing this before "lnetctl net unconfigure" prevents the hang in kiblnd_shutdown(), thanks.

[Serguei Smirnov]

Hi Olaf,

It looks like I'm able to reproduce the issue using similar setup. I was using two routers, routing between ib and tcp networks, and lnet_selftest to generate traffic between the ib server and the tcp client.

I should be able to use this to look further into fixing this properly. In the meantime though, I experimented with executing "lnetctl set routing 0" on the router node before running "lustre_rmmod" on it, which seems to prevent it from getting stuck. I wonder if you can give this extra step a try to see if it helps in your case, too, as a kind of temporary workaround.

Thanks,

Serguei.

[Olaf Faaland]

Hi Serguei,

I performed a test, with https://review.whamcloud.com/46711, and still see "waiting for 1 peers to disconnect".

My reproducer:
1. Start a lustre file system on garter[1-8], on o2ib100 (mlx)
2. Start LNet on 4 routers, mutt[1-4], on o2ib100 and o2ib44 (opa)
3. Mount the file system on 64 clients on o2ib44, which reach garter through mutt[1-4]
4. Start a 64-node 512-task IOR on the clients, writing to all the OSTs
5. Run "systemctl stop lnet" on mutt3
6. I observe "lnetctl lnet unconfigure" is hung as originally reported, and the stack is the same. The console log for mutt3 shows "waiting for 1 peers to disconnect" repeatedly

Just to be sure, note that we are not using MR.

thanks,
Olaf

[Olaf Faaland]

Thanks, Serguei. I hope to test it tomorrow.