In the Linux kernel, the following vulnerability has been resolved:
gpio: ml-ioh: use raw_spinlock_t for the register lock
ioh_irq_type() is registered as the irq_chip .irq_set_type callback and
takes chip->spinlock with spin_lock_irqsave(). This callback is reached
from __setup_irq() -> __irq_set_trigger() -> chip->irq_set_type() while
the caller holds desc->lock, a raw_spinlock_t, with hardirqs disabled.
That context is not sleepable, but on PREEMPT_RT a regular spinlock_t is
an rtmutex-backed sleeping lock, so acquiring it there is invalid.
ioh_irq_enable() and ioh_irq_disable() take the same lock from the
.irq_enable/.irq_disable callbacks, which are likewise invoked with
desc->lock held.
Convert the register lock to raw_spinlock_t. The same lock also
serializes the GPIO direction/value callbacks and the suspend/resume
register save/restore, and those critical sections only perform short
sequences of MMIO register accesses (ioread32()/iowrite32()); the
.irq_set_type callback additionally emits a dev_warn() on an unsupported
type. None of these are sleepable operations, so keeping this register
lock non-sleeping is appropriate for the irqchip callbacks and does not
change the GPIO-side locking contract.
This is the same fix as commit a02b8950d619 ("gpio: pch: use
raw_spinlock_t for the register lock"); this driver shares the same
structure as gpio-pch.