[Bug 1572608] Re: Samba 2:4.3.8+dfsg-0ubuntu0.14.04.2 Reversion: CPU Soft Lock

[Ed Huyer]

I'm pretty sure it's not a RAM thing.  The system I encountered the CPU
soft lockup on has 192GB of RAM, and Zabbix shows it as mostly being
free when the problem occurred.

As an aside, Victor, are you sure this is the same problem you're
having?  Looking at your error log, it appears to be something else?  In
the release notes for the Badlock fixes there were a few new options in
smb.conf that can affect authentication.

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Title:
  Samba 2:4.3.8+dfsg-0ubuntu0.14.04.2 Reversion: CPU Soft Lock

Status in samba package in Ubuntu:
  Confirmed

Bug description:
  Upon upgrading to Samba 4.3.8, I encounter crippling soft lockup
  problems with smbd.  The kernel will start throwing errors (see below)
  about what appears to be the root smbd process, and the locked process
  eventually cripples all smb connections to the server.  Further, the
  process is sufficiently locked that SIGKILL has no effect.  While the
  process is locked, the system shows steadily increasing iowait on the
  CPU.

  /var/log/error excerpt:
  Apr 20 09:34:17 banner kernel: BUG: soft lockup - CPU#7 stuck for 22s! [smbd:9842]
  Apr 20 09:34:45 banner kernel: BUG: soft lockup - CPU#7 stuck for 22s! [smbd:9842]
  Apr 20 09:35:13 banner kernel: BUG: soft lockup - CPU#7 stuck for 22s! [smbd:9842]
  Apr 20 09:35:41 banner kernel: BUG: soft lockup - CPU#7 stuck for 22s! [smbd:9842]
  Apr 20 09:36:09 banner kernel: BUG: soft lockup - CPU#7 stuck for 22s! [smbd:9842]
  Apr 20 09:36:37 banner kernel: BUG: soft lockup - CPU#7 stuck for 22s! [smbd:9842]
  Apr 20 09:36:51 banner kernel: INFO: rcu_sched self-detected stall on CPU { 7}(t=240025 jiffies g=7144731 c=7144730 q=0)

  smb.conf global options:
  [global]
          workgroup = [redacted]
          server string = Samba Server Version %v
          interfaces = lo eth0
          hosts allow = [redacted]
          socket options = SO_SNDBUF=16384 SO_RCVBUF=16384 TCP_NODELAY
          syslog only = yes
          security = ads
          passdb backend = tdbsam
          realm = [redacted]
          winbind nss info = rfc2307
          idmap config * :backend = tdb
          idmap config * :range = 10000000-11000000
          idmap config [redacted]:schema_mode = rfc2307
          idmap config [redacted]:backend = ad
          idmap config [redacted]:range = 1000-9999999
          idmap config [redacted]:default = yes
          winbind use default domain = true
          winbind offline logon = false
          winbind enum users = no
          winbind enum groups = no
          winbind nested groups = yes
          winbind expand groups = 4
          winbind separator = /
          winbind refresh tickets = yes
          kerberos method = secrets and keytab
          template homedir = /home/%U
          template shell = /bin/bash
          vfs objects = acl_xattr
          map acl inherit = yes
          store dos attributes = yes
         server signing = auto
          winbind sealed pipes = false
          require strong key = false
          winbind sealed pipes:[redacted] = true
          require strong key:[redacted] = true
          preferred master = no
          wins support = no
          wins proxy = no
          dns proxy = no
          load printers = no
          cups options = raw

  Release Info:
  Description:    Ubuntu 14.04.4 LTS
  Release:        14.04

  I will also note that the Samba shares are living on Ceph RBD volumes
  formatted as XFS.  It seems unlikely, but it's conceivable that Samba
  4.3.8 introduced some new conflict with the kernel RBD module.

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