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

Summary

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.

Timeline

1. Sep 17, 2026, 4:07 PM UTCCVE published
2. Oct 19, 2026, 8:59 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 0e2a9a03106cd5fa0dbc9047675e7645c55e2669 · fixed in aa482273f32117c3adeba9b1cc945e0b5d33722d; From 0e2a9a03106cd5fa0dbc9047675e7645c55e2669 · fixed in 8b8de6400c86937ed57d680d06d716e167b381de; From 0e2a9a03106cd5fa0dbc9047675e7645c55e2669 · fixed in e40b3edeaf25cd09e9c88edb1ef99373ca37593b; From 0e2a9a03106cd5fa0dbc9047675e7645c55e2669 · fixed in 3690aaa6d18f6775c3e7932fb8af8c5bf6a6b69c

• Linux Linux

  6.11

• KernelLinux

  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

References 4