Centos-6 kernel soft lockup CPU#20 stuck for 67s! [smbd-notifyd] after upgrade form 4.2 to 4.4

Volker Lendecke Volker.Lendecke at SerNet.DE
Mon May 2 13:20:45 UTC 2016

On Mon, May 02, 2016 at 03:08:43PM +0200, Dr. Hansjoerg Maurer wrote:
> we updated a samba server from 4.2.9 to 4.4.2 last week and got today a total system hang with the following message
> kernel: BUG: soft lockup - CPU#20 stuck for 67s! [smbd-notifyd:26402]

That's a kernel bug.

> The system is runnuning under Centos-6 x86_64 with latest updates installed.
> The ext4 filesystem is exported by nfs3  and samba.

Downgrade your kernel.

> I checked the release notes for 4.3.0  and found, that there have been changes in the  FileChangeNotify subsystem

Yes, we are using unix domain datagram sockets more excessively now.
The kernel does not like it, although it is a pretty standard API.

> Does anybody else has problems in this area.
> We will try it again with
>  kernel change notify = no

Won't help. Downgrade Samba to 4.2 and wait for the next CentOS kernel
to fix the issue.


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