Dell Unity: Linux Hosts Mounted using NFSv4.2 on Unity Running OE 5.5 Cause SP Panics

Summary: In Unity 5.5, File System (FS) access can be provided using a Network File System (NFS) mount using NFSv3 or NFSv4 file sharing protocols. This is typically done for Logical Unity Numbers (LUN) and NFS datastores with specific mounting parameters and then scripted for various groups of hosts. A directory is created for the mount point when mounting file shares using NFSv4.2. If the directory security label (sec_label) parameter has no data assigned to it, the Unity Service Processors (SP) can panic and reboot unexpectedly. ...

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Symptoms

In Unity OE 5.5, support for NFSv4.2 was added with mode and sec_label parameters to be used during the NFS mounting process.

  • In certain NFSv4.2 script mounting scenarios to create a directory for the mount point, if the sec_label has no data assigned to it, the Unity System Processors (SP) can encounter a SIGSEGV panic and reboot unexpectedly. 
  • One or both SPs can panic due to a race condition between a rename and a directory listing. This can cause the system to go down and one or both SPs to come up in rescue-mode.

Sample panic output from Unity logs:

B       05/14/25 19:01:09                           CSX RT: panic requested at: <file-unknown>:0 (thread: 139634334762752 aka 139634334762752) [PID:7138 TID:9862 CORE:1 [csx_ic_std.x] [nfs09_007] [05/14/2025 19:01:09 UTC]] (panic action:DEFAULT expr:<no-expr> flags:-) [info:0]
B       05/14/25 19:01:09                           CSX RT: Fatal: Process received SIGSEGV:
B       05/14/25 19:01:09                           SIGSEGV(SEGV_MAPERR)@0x20
B       05/14/25 19:01:09                           CSX RT: panic backtrace: [26ec0700] 00007f159e87ab34 <csx_rt_proc_request_backtrace +0x00000154> (sp=00007f159eb45440) proc=7f159e87a9e0-7f159e87b01d csx_urt.so
B       05/14/25 19:01:09                           CSX RT: panic backtrace: [26ec0700] 00007f159e846a27 <csx_rt_assert_request_panic +0x000000b7> (sp=00007f159eb46380) proc=7f159e846970-7f159e846a3b csx_urt.so
B       05/14/25 19:01:09                           CSX RT: panic backtrace: [26ec0700] 00007f159e878727 <csx_rt_proc_int_handle_fatal_signal +0x000002d7> (sp=00007f159eb464a0) proc=7f159e878450-7f159e8788f2 csx_urt.so
B       05/14/25 19:01:09                           CSX RT: panic backtrace: [26ec0700] 00007f159e87d543 <csx_rt_proc_int_handle_sigsegv +0x000001b3> (sp=00007f159eb46520) proc=7f159e87d390-7f159e87d597 csx_urt.so
B       05/14/25 19:01:09                           CSX RT: panic backtrace: [26ec0700] 00007f1545d20ea9 <_ZN13nfs4_attrhold17nfs4SetattrVerifyEjRPj+0x00000049> (sp=00007eff26ebed10) proc=7f1545d20e60-7f1545d20f90 cdx.so
B       05/14/25 19:01:09                           CSX RT: panic backtrace: [26ec0700] 00007f1545d217be <_Z13nfs4_secLabeliiP14nfs4_attr_infoP8nfs4_ctxP13nfs4_attrholdP15File_NamingNodeP17Access_Credential+0x0000075e> (sp=00007eff26ebed60) proc=7f1545d21060-7f1545d21823 cdx.so

Note: The panics do not happen on every NFSv4.2 mounting attempt and some work without issue. 

If SP panics occur, contact Dell Support and reference this article to investigate the status of the system. Do not attempt to troubleshoot the SPs without support's guidance.

Cause

The current Unity OE 5.5 code cannot handle the sec_label attribute without data assigned. As a result, the SP accesses a null memory pointer causing a SIGSEGV panic.  Additionally, 5.5 code can encounter a race condition between a directory listing and a rename operation, resulting in blocked threads and a watchdog timeout panic.

 

Resolution

Fix:

The race condition is fixed in Dell Unity OE Version 5.5.2.  Please upgrade to this version in order to fix this issue.

The blank sec_label issue is still being addressed by Engineering.  Watch this Knowledgebase article for further updates.  In the meantime, the Workarounds below can work around the blank sec_label issue.

 

Workaround:

Use the following article to disable the NFSv4.2 Security Label: 

The article also shows the following workarounds, which will also work around both of these issues:

  • Mount the Linux servers using NFSv3, NFSv4, or NFSv4.1 only
  • Parameter to downgrade the max supported NFSv4 version to 4.1

Additional Information

An NFSv4.2 mount point directory "create request" on a Linux host that provides mode and sec_label information impacts the request in the following ways:

  • Mode: This parameter specifies the permissions for the new directory. It defines the read, write, and run permissions for the owner, group, and others. For example, a mode of 0755 grants read, write, and run permissions to the owner, and read and run permissions to the group and others. This ensures that the directory is created with the correct access controls.
  • Sec_label: This parameter is used to apply security labels to the directory. Sec_labels are part of the Mandatory Access Control (MAC) system, which provides finer-grained access control compared to traditional Discretionary Access Control (DAC). When a directory is created with a sec_label, the NFS server stores and retrieves these labels, ensuring that the directory adheres to the specified security policies.

This is useful in environments requiring strict security compliance. 

This article discusses what a SIGSEGV memory panic is: Dell Unity: Storage Processor has encountered panic with cause SIGSEGV

Affected Products

Dell EMC Unity
Article Properties
Article Number: 000334226
Article Type: Solution
Last Modified: 31 Oct 2025
Version:  5
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