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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
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.
Sources
Also known as BELL-CVE-2026-90193, DEBIAN-CVE-2026-90193, GHSA-vrrh-vfw6-8f53, UBUNTU-CVE-2026-90193.