CVE-2026-90193

/// Technical 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

insi

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References