Osdtrace Not Working With Rook: Troubleshooting & Debugging

by Alex Johnson 60 views

If you're encountering issues with osdtrace in your Rook cluster, you're not alone. This article dives deep into a common problem faced by users trying to leverage osdtrace for Ceph OSD tracing within a Rook environment, specifically with Ceph version 18.2.7. We'll explore the error messages, potential causes, and step-by-step solutions to get osdtrace working correctly. Let's get started on how to troubleshoot and debug this issue effectively.

Understanding the Problem: osdtrace Timeout and Dwarf Errors

The user reported an issue while running osdtrace on a Rook cluster with Ceph version 18.2.7. The tool, designed for tracing Ceph OSD operations, produced a timeout error and indicated problems with dwarf debug symbols. Here's a breakdown of the situation, starting with the user's context:

The user was trying to use osdtrace on a Rook cluster, which is a popular open-source cloud-native storage orchestrator for Kubernetes. They were running Ceph version 18.2.7. The user's understanding was that osdtrace should run on bare metal rather than in a container, which is a key point to consider for troubleshooting.

Decoding the Error Messages

When the user executed osdtrace -x -t 10 (with a 10-second timeout), the following output was observed:

Execution timeout set to 10 seconds.
Start to parse ceph dwarf info
Found executable ceph-osd at: /usr/bin/ceph-osd
Tracing ceph-osd at: /usr/bin/ceph-osd
preprocess_module dwarf get error
Please ensure the debug symbol is installed
handle_module dwarf get error
Start to load uprobe
BPF prog loaded
uprobe OSD::dequeue_op attached
uprobe PrimaryLogPG::execute_ctx attached
uprobe ECBackend::submit_transaction attached
uprobe OpRequest::mark_flag_point_string attached
uprobe OpRequest::mark_flag_point attached
uprobe ReplicatedBackend::generate_subop attached
uprobe ReplicatedBackend::do_repop_reply attached
uprobe BlueStore::queue_transactions attached
uprobe BlueStore::_txc_calc_cost attached
uprobe BlueStore::_txc_state_proc attached
uprobe PrimaryLogPG::log_op_stats attached
uprobe ReplicatedBackend::repop_commit attached
uprobe OSD::enqueue_op attached
New a ring buffer
Started to poll from ring buffer
Timeout occurred. Exiting.
Unexpected line hit
Clean up the eBPF program

This output reveals several crucial pieces of information:

  • Dwarf Errors: The lines preprocess_module dwarf get error and handle_module dwarf get error strongly suggest an issue with the debug symbols (dwarf) required by osdtrace. Debug symbols are essential for tools like osdtrace to map program code to its source, enabling effective tracing. The message Please ensure the debug symbol is installed is a direct hint.
  • Timeout: The Timeout occurred. Exiting. message indicates that osdtrace didn't receive the expected data within the specified 10-second timeout period. This could be due to several factors, including the dwarf symbol issue preventing proper tracing, or underlying problems with the OSD operations themselves.
  • Uprobe Attachment: The tool successfully attached several uprobes (userspace probes) to various Ceph OSD functions (e.g., OSD::dequeue_op, PrimaryLogPG::execute_ctx). This suggests that the basic tracing mechanism is working, but the lack of data being captured points to a deeper problem.

The user also mentioned that attempting to connect to a specific OSD using the -p flag yielded the same result, reinforcing the notion that the issue is systemic rather than isolated to a particular OSD instance.

Key Takeaways

  1. Missing Debug Symbols: The primary error points to missing or inaccessible debug symbols for the ceph-osd executable.
  2. Timeout Issue: The timeout suggests that osdtrace is not receiving the expected trace data, likely due to the debug symbol problem.
  3. Systemic Problem: The issue affects all OSDs, indicating a configuration or environmental problem rather than an isolated OSD failure.

Diagnosing the Root Cause: Why Are Debug Symbols Missing?

To effectively troubleshoot, we need to understand why osdtrace can't find the necessary debug symbols. Several factors could contribute to this:

  1. Missing Debug Packages: In many Linux distributions, debug symbols are not included in the default packages for performance and size reasons. They are often provided in separate -dbg or -debuginfo packages.
  2. Incorrect Installation: Even if the debug packages are installed, they might not be in the expected location or might not be properly linked to the ceph-osd executable.
  3. Containerization Issues: If osdtrace is being run inside a container (contrary to the user's understanding), the debug symbols might not be present within the container image.
  4. Version Mismatch: The debug symbols must match the exact version of the ceph-osd executable. If there's a mismatch, osdtrace will fail to interpret the symbols correctly.
  5. Dwarf Information Availability: The user's question, “Also, no dwarf for 18 branch?” highlights a crucial concern. Debug symbols (dwarf information) might not be readily available or properly packaged for specific Ceph branches or versions.

Step-by-Step Troubleshooting and Solutions

Here’s a structured approach to resolving the osdtrace issue, incorporating the user’s context and the diagnostic insights:

Step 1: Verify osdtrace Execution Environment

The user correctly assumed that osdtrace should ideally run on bare metal (or at least in the same environment as the Ceph OSD processes) rather than in a separate container. This is because osdtrace needs direct access to the ceph-osd executable and its associated libraries and debug symbols. However, let's confirm this:

  • Check Execution Context: Ensure that you are running osdtrace on the same host where the ceph-osd processes are running. If using Kubernetes and Rook, this typically means running osdtrace within one of the OSD pods or on a node where OSDs are running.
  • Kubernetes Exec: If running within Kubernetes, use kubectl exec -it <pod-name> -- bash to enter the OSD pod and run osdtrace from there.

Step 2: Install Debug Symbols

This is the most likely solution, given the error messages. You need to install the debug symbols for the ceph-osd executable. The exact steps depend on your Linux distribution:

  • Debian/Ubuntu:

    sudo apt update
sudo apt install ceph-osd-dbg

    This command installs the ceph-osd-dbg package, which contains the debug symbols. Ensure that the package version matches your Ceph version (18.2.7 in this case). You might need to add the Ceph repository to your APT sources if it's not already configured.

  • CentOS/RHEL:

    sudo yum install yum-plugin-debuginfo
sudo debuginfo-install ceph-osd

    These commands install the yum-plugin-debuginfo plugin and then use it to install the debug symbols for ceph-osd. Again, ensure the Ceph repository is correctly configured.

  • Direct Download (if packages are unavailable): If the debug packages are not readily available through your distribution's package manager, you might need to download them directly from the Ceph repository or build them yourself. This is a more advanced approach and requires familiarity with Ceph build processes.

Step 3: Verify Debug Symbol Installation

After installing the debug symbols, verify that they are correctly installed and accessible. You can use the gdb (GNU Debugger) to check this:

  1. Run GDB:

    gdb /usr/bin/ceph-osd

  2. Check Symbols: Inside GDB, use the info functions command. This should list the functions in ceph-osd along with their addresses. If the symbols are correctly loaded, you'll see a detailed list of functions.

    If you encounter errors or the list is incomplete, the debug symbols are not properly loaded.

Step 4: Address Potential Version Mismatch

Ensure that the debug symbols you installed match the exact version of the ceph-osd executable. A version mismatch can lead to incorrect tracing and dwarf errors.

  • Check Ceph Version: Use ceph -v to determine the Ceph version.
  • Verify Package Version: Check the version of the installed debug package (e.g., using dpkg -l ceph-osd-dbg on Debian/Ubuntu or rpm -q ceph-osd-debuginfo on CentOS/RHEL).
  • Reinstall if Necessary: If there's a mismatch, reinstall the correct debug package version.

Step 5: Investigate Containerization (If Applicable)

Although the user believes osdtrace should run outside a container, it's worth double-checking, especially in a Kubernetes environment. If osdtrace is inadvertently running inside a container:

  • Verify Pod Context: Confirm that you are executing osdtrace within the correct pod or on the host where the OSD processes are running.
  • Container Image: Ensure that the container image used for the OSD pods includes the debug symbols. If not, you'll need to rebuild the image with the debug packages installed.

Step 6: Adjust Timeout (If Necessary)

If the debug symbols are correctly installed but you still encounter timeouts, the 10-second timeout might be too short for your environment. Try increasing the timeout value using the -t flag:

./osdtrace -x -t 30

A longer timeout gives osdtrace more time to capture trace data, especially in busy clusters.

Step 7: Consider Kernel Version and eBPF Compatibility

osdtrace relies on eBPF (Extended Berkeley Packet Filter) technology, which has specific kernel requirements. Ensure that your kernel version supports the necessary eBPF features.

  • Kernel Version: eBPF features are generally well-supported in kernels 4.9 and later. Check your kernel version using uname -r.
  • eBPF Tools: Verify that you have the necessary eBPF tools installed (e.g., bpftool).

Step 8: Address the "No Dwarf for 18 Branch?" Concern

The user's question about the availability of dwarf information for the 18 branch is pertinent. While debug symbols should ideally be available for all Ceph releases, there might be instances where they are not readily packaged or easily accessible.

  • Ceph Repositories: Check the official Ceph repositories for debug packages specific to the 18.2.7 release. If they are not available, you might need to build them yourself.
  • Ceph Community: Engage with the Ceph community (forums, mailing lists, or the Rook community if applicable) to inquire about the availability of debug symbols for your specific Ceph version. Other users might have encountered the same issue and found a solution.

Step 9: Simplify the Command

Try running osdtrace with the most basic command to rule out any issues with specific flags or options:

./osdtrace

If this works, you can then add flags one by one to identify any problematic options.

Conclusion: Persistence and Community Support

Troubleshooting osdtrace issues, especially in complex environments like Rook and Ceph, can be challenging. The key is to systematically address potential causes, starting with the most likely culprits (like missing debug symbols) and progressively investigating other factors.

In the user's case, the most probable cause is the missing debug symbols for ceph-osd. Installing the appropriate debug packages should be the first step. If the problem persists, the other troubleshooting steps outlined above will help narrow down the issue.

Remember, the Ceph and Rook communities are valuable resources. Don't hesitate to seek help from other users and developers if you encounter roadblocks. Providing detailed information about your environment, the steps you've taken, and the errors you're seeing will greatly assist in finding a solution.

For more information on Ceph and Rook, consider visiting the official Ceph Documentation for comprehensive guides and resources.