Recently we encountered an issue with NFS drive getting stuck and causing problem with our cluster nodes. Here is the detailed error logs about the issue when the drive was not responding.
[Fri Aug 10 14:20:17 2024] </TASK>
[Fri Aug 10 14:22:18 2024] INFO: task nfsd:1525 blocked for more than 241 seconds.
[Fri Aug 10 14:22:18 2024] Not tainted 6.1.0-21-amd64 #1 Debian 6.1.90-1
[Fri Aug 10 14:22:18 2024] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[Fri Aug 10 14:22:18 2024] task:nfsd state:D stack:0 pid:1525 ppid:2 flags:0x00004000
[Fri Aug 10 14:22:18 2024] Call Trace:
[Fri Aug 10 14:22:18 2024] <TASK>
The error `echo 0 > /proc/sys/kernel/hung_task_timeout_secs` suggests that the system is experiencing issues related to "hung tasks." A hung task in the Linux kernel is a task (or process) that has been running for an excessively long time without yielding control back to the scheduler, indicating it might be stuck or hung.
Here’s a breakdown of what this message means and potential steps to address it:
Understanding the Message:
1. Hung Task Timeout: The kernel parameter `hung_task_timeout_secs` defines the time (in seconds) after which the kernel will consider a task as hung if it has not been scheduled out. Setting this value to `0` disables the detection of hung tasks, which is not recommended unless you’re troubleshooting or dealing with a specific issue.
2. Error Implication: If the system is logging this message, it might mean that the hung task detection is triggered, and some tasks are taking too long to execute. This could be due to high I/O wait times, a disk failure (as you mentioned RAID issues earlier), or other performance bottlenecks.
Causes and Troubleshooting Steps:
1. Disk I/O Issues: If the RAID array is degraded or experiencing issues, it can lead to increased I/O wait times, causing tasks to hang while waiting for disk operations to complete. Monitor disk I/O performance using tools like `iostat`, `iotop`, or `dstat`.
2. High System Load: Check the system load (`uptime` or `top`). If the system is under heavy load, especially due to CPU or memory pressure, tasks might be delayed or hung.
3. Filesystem Issues: Corruption or problems in the filesystem could also cause tasks to hang. Run `dmesg` to check for any filesystem-related errors or warnings.
4. NFS or Network Issues: If your system is relying on NFS and the underlying network is slow or experiencing issues, tasks waiting on NFS operations might hang.
5. Kernel Bugs or Misconfigurations: In rare cases, bugs in the kernel or misconfigured kernel parameters could lead to hung tasks. Ensure that your kernel is up-to-date, and check for any known issues with the kernel version you're using.
Mitigation:
1. Increase the Timeout Value: If you’re dealing with temporary performance issues, you can increase the `hung_task_timeout_secs` value to give the system more time before considering tasks as hung. For example, setting it to 300 seconds (5 minutes) might help if you believe the issue is temporary.
echo 300 > /proc/sys/kernel/hung_task_timeout_secs
You can also make this change permanent by adding it to `/etc/sysctl.conf`:
kernel.hung_task_timeout_secs = 300
2. Disable Hung Task Detection Temporarily: If you are troubleshooting and need to disable the detection temporarily, you can set the value to `0` as indicated by the log:
echo 0 > /proc/sys/kernel/hung_task_timeout_secs
3. Investigate the Root Cause: Instead of just silencing the error, it’s crucial to find and fix the underlying issue. Start by examining system logs (`/var/log/messages` or `/var/log/syslog`) and use monitoring tools to identify potential bottlenecks.
4. Replace Faulty Hardware: If this issue is linked to a failing RAID disk which indeed was in our case as one of disk appeared to be failed, replace the faulty drive and rebuilt the array as needed.
Addressing the underlying cause of the hung tasks is essential to prevent further disruptions.
