# CVE-2026-90193: mailbox: qcom-cpucp: fix PREEMPT_RT self-deadlock in IRQ handler

> A self-deadlock in the Qualcomm CPUCP mailbox driver under PREEMPT_RT causes a permanent system hang, requiring a kernel patch.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-90193, DEBIAN-CVE-2026-90193, GHSA-vrrh-vfw6-8f53, UBUNTU-CVE-2026-90193

## What is CVE-2026-90193?

CVE-2026-90193 is a vulnerability in Linux, published on 17 Sep 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:

mailbox: qcom-cpucp: fix PREEMPT_RT self-deadlock in IRQ handler

qcom_cpucp_mbox_irq_fn() calls mbox_chan_received_data() while holding
chan->lock. Under PREEMPT_RT, spin_lock_irqsave() is converted to an
rt_spinlock (rtmutex-based), which tracks ownership and can sleep.

The callback chain triggered by mbox_chan_received_data() eventually
reaches mailbox_clear_channel() -> mbox_send_message() -> add_to_rbuf(),
which attempts to re-acquire the same chan->lock. Since rtmutex detects
the re-entrant lock attempt by the same owner, the thread blocks waiting
for a lock it already holds, causing a permanent deadlock.

This deadlock manifests as 'irq/N-apss_cpucp_mbox' stuck in D state
with the following call trace:
  rt_spin_lock -> mbox_send_message -> mailbox_clear_channel ->
  scmi_rx_callback -> mbox_chan_received_data [<- held chan->lock here]

Fix by saving chan->cl locally and clearing the HW interrupt register
inside the lock, then invoking mbox_chan_received_data() after releasing
the lock. This preserves the mutual exclusion for chan->cl access while
avoiding the lock re-entrancy that causes the PREEMPT_RT deadlock.

## Which versions are affected by CVE-2026-90193?


## How do I fix CVE-2026-90193?

Apply the vendor's patch.

## Is CVE-2026-90193 being exploited?

There is no known exploitation of CVE-2026-90193 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90193 and fix it if it is affected.

What it is: CVE-2026-90193 is a vulnerability in Linux, published on 17 Sep 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-2026-90193 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-2026-90193/ (Markdown: https://insights.sbomify.com/CVE-2026-90193/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90193
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90193
- OSV: https://osv.dev/vulnerability/CVE-2026-90193

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90193/
Summaries are generated and may contain mistakes; the official description above is the record.