# CVE-2026-74638: drm/v3d: Serialize the scheduler timeout handlers > A race condition in the Linux kernel V3D GPU driver allows local attackers to trigger a system warning and potential denial of service via concurrent scheduler timeouts. - **Severity:** Not scored - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 22 Aug 2026 - **Updated:** 25 Aug 2026 - **Also known as:** BELL-CVE-2026-74638, DEBIAN-CVE-2026-74638, GHSA-g887-j6m8-c6gc, UBUNTU-CVE-2026-74638 ## What is CVE-2026-74638? CVE-2026-74638 is a vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description In the Linux kernel, the following vulnerability has been resolved: drm/v3d: Serialize the scheduler timeout handlers V3D exposes several independent hardware queues (BIN, RENDER, TFU and CSD) but has only a single, global reset. A timeout on any one queue therefore has to stop, reset and restart the schedulers of every other queue as well. That makes concurrent timeout handlers unsafe. `reset_lock` was never able to make them safe, as a driver-side lock can only cover the driver's &drm_sched_backend_ops.timedout_job callback. The scheduler handles the timed out job and its pending list around that callback, outside of the driver's control, so a global reset triggered by one queue can still interfere with another queue that is in the middle of handling a timeout of its own. Consequently, if a reset happens in the CSD queue while a CL-intensive application is running, the global reset stops and restarts the CL queue's scheduler while that queue is handling a timeout of its own. As drm_sched_stop() and drm_sched_start() subtract and add the credits of every job sitting on the pending list of the scheduler they are called on, and as the CL queue's handler concurrently takes its job off that same list and puts it back, the stop and the start no longer see the same set of jobs. The CL queue is left with more credits in flight than its limit: [ 327.302739] ------------[ cut here ]------------ [ 327.302744] WARNING: CPU: 2 PID: 43 at drivers/gpu/drm/scheduler/sched_main.c:102 drm_sched_run_job_work+0x238/0x4d0 [gpu_sched] [ 327.302884] CPU: 2 UID: 0 PID: 43 Comm: kworker/u16:1 Not tainted 6.18.39-v8-16k+ #3 PREEMPT [ 327.302889] Hardware name: Raspberry Pi 5 Model B Rev 1.0 (DT) [ 327.302893] Workqueue: v3d_bin drm_sched_run_job_work [gpu_sched] [ 327.302984] Call trace: [ 327.302987] drm_sched_run_job_work+0x238/0x4d0 [gpu_sched] (P) [ 327.302997] process_scheduled_works+0x180/0x3d0 [ 327.303010] worker_thread+0x268/0x3e8 [ 327.303016] kthread+0x140/0x250 [ 327.303022] ret_from_fork+0x10/0x20 [ 327.303031] ---[ end trace 0000000000000000 ]--- From that point on, the credit count of the CL queue is broken, causing a complete GPU hang and UI freeze. The DRM scheduler already provides a mechanism to serialize the timeout handlers of different schedulers: an ordered workqueue passed as drm_sched_init()'s @timeout_wq parameter. By default, each scheduler queues its timeout work on the system workqueue, which runs the handlers concurrently. Give all of the queues a shared ordered workqueue instead, as recommended by the DRM scheduler documentation for hardware that has distinct queues but resets globally. ## Which versions are affected by CVE-2026-74638? ## How do I fix CVE-2026-74638? Apply the vendor's patch. ## Is CVE-2026-74638 being exploited? There is no known exploitation of CVE-2026-74638 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-74638 and fix it if it is affected. What it is: CVE-2026-74638 is a vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-74638 in the wild and no public exploit code. Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-74638/ (Markdown: https://insights.sbomify.com/CVE-2026-74638/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74638 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74638 - OSV: https://osv.dev/vulnerability/CVE-2026-74638 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-74638/ Summaries are generated and may contain mistakes; the official description above is the record.