Fixing GPU Stalls & Segfaults In TheRock 7.11.0a

Hey everyone! Today, we're diving deep into a rather frustrating issue that's been popping up in our CI pipelines, specifically affecting GPU workloads when using TheRock version 7.11.0a20251201. We're talking about those pesky GPU stalls and occasional segfaults that bring our builds to a screeching halt. It's like your graphics card decides to take an unscheduled nap right when you need it most, or worse, throws a segmentation fault, which is basically its way of saying "I don't know what to do anymore!" This problem seems to be particularly prevalent in the fusilli project, where tests are timing out or failing with these critical errors. We've seen examples in GitHub Actions, like this one: https://github.com/iree-org/fusilli/actions/runs/19954005561/job/57219452177. Even when running locally, tests that should complete in about 10-15 seconds are showing timeouts, even though the timeout is set generously at 120 seconds. This isn't a case of the timeout being too short; increasing it doesn't solve the underlying flake. It's been observed on the main branch too, not just in specific PRs, which means it's something we need to actively bisect and fix. So far, it seems to primarily impact GPU workflows, not CPU-only runs, which is a crucial clue. The problem appears randomly with different tests, and often it's the last one to run in a concurrent batch that triggers the issue. One key observation is that during these "stuck" states, the GPU's SCLK (using rocm-smi) shows an unusually high clock speed, around 2100 MHz. As soon as we managed to kill the process, the clock speed dropped back to the default idle speed of 132 MHz. This strongly suggests that the GPU isn't properly cleaning up or releasing resources after a task, leading to this high-frequency, unresponsive state. In some cases, this leads to a more severe outcome: a segfault. We've seen this in the fusilli project as well, like in this CI run: https://github.com/iree-org/fusilli/actions/runs/19836981433/job/56836514364, where tests like fusilli_pointwise_samples_pointwise_unary_ops fail with a SIGSEGV – a segmentation violation signal. This is a serious error indicating that the program tried to access memory it shouldn't have, often a symptom of underlying driver or resource management issues. The goal here is to figure out what's causing these stalls and segfaults and get our GPU builds running smoothly again.

Unpacking the Bisection: Pinpointing the Culprit

Okay guys, let's talk about how we narrowed down the source of this gnarly GPU stall and segfault problem. This wasn't a straightforward fix, and it took some serious bisection detective work. Initially, when we looked at the fusilli repository, the bisection pointed to a commit where both IREE and TheRock were bumped. This happened between the 11/12 nightly build and the 12/1 nightly build. To figure out which component was the real troublemaker, we ran further bisecting experiments along the IREE nightlies. What we found was interesting: running with IREE version 3.10.0rc20251201 didn't reproduce the stall or segfault issue. This was a big hint! It meant that simply bumping IREE wasn't the sole cause. The next step was to isolate the impact of TheRock. We know that the commit in question involved bumping TheRock from 7.10.0a20251112 to 7.11.0a20251201. So, we decided to run ablation experiments, essentially testing each component upgrade separately. In the first experiment, we used IREE at 3.9.0rc20251112 but bumped only TheRock to 7.11.0a20251201. The results? We saw the GPU stalls and segfaults reappearing, happening in about 12 out of 20 runs (https://github.com/iree-org/fusilli/actions/runs/19991537909). This was a strong indicator that TheRock 7.11.0a20251201 was indeed involved. For the second experiment, we did the opposite: we kept TheRock at the older version 7.10.0a20251112 and bumped only IREE to 3.10.0rc20251201. The outcome here was completely different – no stalls or segfaults whatsoever! All 20 runs passed (https://github.com/iree-org/fusilli/actions/runs/19991551345). This confirmed our suspicion: the issue isn't with IREE itself, but rather something introduced or changed in TheRock version 7.11.0a20251201. This points us towards a potential problem within the ROCm driver or HIP layer, specific to this version of TheRock. It's crucial for us to understand why this particular version is causing resource cleanup issues or state corruption on the GPU, leading to these stalls and crashes. The next steps involve digging deeper into the ROCm/HIP components to identify the exact code path or behavior change that triggers this instability. We need to figure out if it's a bug in the driver, a compatibility issue with how IREE interacts with it, or perhaps a subtle change in TheRock's internal workings that affects GPU resource management during cleanup phases. This detailed bisection process is vital for us to move forward and develop a robust solution, ensuring our GPU workflows are stable and reliable.

System and Configuration Details

Alright team, let's lay out the specs of the system where we're seeing these GPU stalls and segfaults when using TheRock 7.11.0a20251201. Understanding the environment is super important for debugging these kinds of low-level hardware and driver issues. We're running this on a pretty beefy machine running Ubuntu VERSION="24.04.3 LTS (Noble Numbat)". This is the latest LTS release from Ubuntu, so we're generally on a modern and supported OS. The CPU is an AMD EPYC 9554 64-Core Processor. This is a high-performance server-grade CPU, and while it's powerful, it's not typically the source of GPU-related problems unless there's a very specific interaction. The main player here, of course, is the AMD Instinct MI300X GPU. This is a powerful accelerator designed for compute-intensive workloads, and it's the component that's misbehaving. The ROCm Version we're specifically targeting with this issue is TheRock ~ 7.11.0a20251201. As we've discussed, this version seems to be the trigger for the problems we're observing. We haven't identified a specific ROCm component as the culprit yet, hence the _No response_ in the ROCm Component section of the original report. This means the issue could be anywhere within the ROCm stack – from the kernel drivers to the HIP runtime or even specific libraries used by TheRock. The operating system, Ubuntu 24.04.3 LTS, is quite standard for this kind of development and testing. The EPYC processor, while powerful, isn't usually implicated in GPU stalls unless there's a complex interplay, which is less likely than a driver or firmware issue. The focus really is on the MI300X GPU and the ROCm 7.11.0a20251201 stack. When it comes to reproducing this issue, it's been a bit tricky to get a single, isolated test case that reliably triggers the problem on demand outside of the CI environment. However, the fact that it hits consistently, around 40-50% of the runs in the Fusilli CI, tells us it's not a rare fluke but a reproducible, albeit non-deterministic, issue. We haven't yet gathered the output of /opt/rocm/bin/rocminfo --support, but this is definitely a command we'll be running to get more detailed information about the ROCm installation and its capabilities. This information is vital for understanding the precise configuration of the ROCm environment and for comparing it against known working or non-working configurations. So, to recap, we've got a high-end AMD GPU setup on a recent Ubuntu LTS, running a specific version of ROCm (TheRock 7.11.0a20251201) that's causing intermittent but significant problems. The next steps are to delve into the specifics of the ROCm installation and potentially look for known issues or bugs related to this version of TheRock or the MI300X on Ubuntu 24.04.

Reproducing the Problem: A CI Conundrum

So, you want to know how to make these GPU stalls and segfaults happen with TheRock 7.11.0a20251201? Honestly guys, that's the million-dollar question right now! As we've seen, reproducing this issue reliably on demand, outside of our Continuous Integration (CI) environment, has been a bit of a challenge. The problem manifests as a flake, meaning it doesn't happen every single time, but often enough to be a serious concern. We're talking about a hit rate of roughly 40-50% in the Fusilli CI runs. This kind of intermittent behavior is notoriously tricky to debug because you can't just run a single command and expect the error to appear. You might run the same test suite multiple times, and it passes perfectly one time, then fails dramatically the next. The original report notes, "I don't know what's the best way to get a good isolated repro but this hits pretty consistently (~40-50% of the runs) in Fusilli CI." This means our best bet for seeing the problem is to observe it in the context of the Fusilli project's automated tests. The tests that seem to be affected are typically those involving pointwise operations, both unary and binary, using the AMDGPU backend. These tests involve compiling MLIR code with iree-compile targeting ROCm, then running the compiled module on the GPU. The timeout occurs after the compilation is reported as successful and the graph execution logs seem to complete, but the test runner still flags it as a timeout. Or, as we've seen, it crashes with a SIGSEGV during the cleanup phase. The non-deterministic nature suggests that the issue might be related to race conditions, resource contention, or specific timing dependencies within the GPU driver or hardware that aren't consistently hit. It could be that certain sequences of operations, memory allocations, or kernel launches are more likely to trigger a bug in TheRock 7.11.0a20251201 under specific, perhaps slightly variable, system load conditions. To try and reproduce it locally, one would need to set up a similar environment: Ubuntu 24.04.3 LTS, an AMD Instinct MI300X GPU, and the ROCm 7.11.0a20251201 stack. Then, they would need to run the Fusilli test suite, possibly focusing on the pointwise_samples tests. Given the flake nature, this would likely involve running the tests multiple times, perhaps in parallel, to increase the chances of hitting the problematic scenario. We're also considering ways to make the reproduction more robust, perhaps by introducing artificial delays or stress patterns in the execution flow, but that requires a deeper understanding of the root cause. For now, the most consistent way to observe the problem is by monitoring the Fusilli CI runs. If you're trying to debug this yourself, hitting the CI and looking at the failed runs provides the clearest evidence of the issue. We're hoping that by sharing this information, someone might be able to set up a more controlled reproduction environment or identify the specific conditions that trigger these GPU stalls and segfaults. It's a puzzle, and the lack of a simple repro.sh script makes it a bit harder, but the CI data is our best lead.

Next Steps: Deep Dive into ROCm and HIP

So, we've identified that TheRock 7.11.0a20251201 is the likely culprit behind those GPU stalls and segfaults we've been seeing. Now, the big question is: what do we do about it? The next logical step, guys, is to dive deep into the ROCm and HIP components. Since our bisection clearly points to TheRock as the source, the issue is almost certainly within AMD's GPU driver stack or the HIP runtime library itself. We need to treat this as a potential bug within ROCm. Here’s a breakdown of what that means and what we should be looking for:

1. Investigate ROCm/HIP API Usage: We need to meticulously review how IREE (or whatever software is triggering the issue) interacts with the HIP API, especially during resource cleanup. The observation that the GPU clocks stay high even when the test appears finished, and the segfaults occurring during cleanup, strongly suggests an issue with how resources (like memory buffers, command queues, or kernels) are being released or de-initialized. Are there any dangling pointers? Are resources being freed before they are fully utilized or after they have been invalidated? We need to check for common pitfalls in GPU programming, such as incorrect synchronization or improper handling of asynchronous operations.

2. Check ROCm Release Notes and Known Issues: For TheRock 7.11.0a20251201, we should scour the official release notes and any associated bug trackers or forums for reported issues related to GPU hangs, stalls, or segfaults, particularly on the AMD Instinct MI300X platform or with Ubuntu 24.04.3 LTS. It's possible this is a known bug that has a workaround or is slated for a fix in a later release.

3. Gather More Diagnostic Information: When the stall occurs, if possible, we need to capture more detailed diagnostic information. Running rocminfo --support (as mentioned in the optional section) is crucial. Additionally, using tools like roctracer or hip_trace might help profile the execution and pinpoint the exact HIP API calls that precede the stall or crash. Analyzing the output of rocm-smi for more than just clock speed – like memory usage, power draw, and thermal throttling – could also provide clues.

4. Isolate the Triggering Operation: If we can identify a specific operation or sequence of operations within the fusilli tests (or any other workload) that consistently triggers the issue, that would be a massive step forward. This might involve simplifying the MLIR kernels or the IREE dispatch logic to create a minimal reproducible example that still exhibits the stall or segfault. This minimal example would be invaluable for reporting the bug to AMD or for further internal debugging.

5. Consider Driver/Firmware Updates: While we are specifically targeting TheRock 7.11.0a20251201, it's worth checking if there are any newer (or even specific older) driver/firmware versions for the MI300X that are known to be more stable. Sometimes, a specific version introduces regressions, and rolling back or upgrading might be a temporary solution.

6. Report the Bug to AMD: If, after investigation, it seems like a genuine bug within the ROCm stack, the next step is to file a detailed bug report with AMD. This report should include all the system details, the ROCm version, the problematic workload (if isolatable), and any diagnostic information gathered. Providing clear steps to reproduce, even if they are