With enabled threaded interrupts the nouveau driver reported the
following:

| Chain exists of:
|   &mm->mmap_lock#2 --> &device->mutex --> &cpuset_rwsem
|
|  Possible unsafe locking scenario:
|
|        CPU0                    CPU1
|        ----                    ----
|   lock(&cpuset_rwsem);
|                                lock(&device->mutex);
|                                lock(&cpuset_rwsem);
|   lock(&mm->mmap_lock#2);

The device->mutex is nvkm_device::mutex.

Unblocking the lockchain at `cpuset_rwsem' is probably the easiest
thing to do.  Move the priority assignment to the start of the newly
created thread.

Fixes: 710da3c8ea7df ("sched/core: Prevent race condition between cpuset and __sched_setscheduler()")
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: Patch description]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/a23a826af7c108ea5651e73b8fbae5e653f16e86.camel@gmx.de

On RT kernels, the use of migrate_disable()/migrate_enable() is sufficient
to guarantee a task isn't moved to another CPU.  Update the
irq_set_irqchip_state() documentation to reflect this.

Signed-off-by: Josh Cartwright <joshc@ni.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210917103055.92150-1-bigeasy@linutronix.de

Fixes: 61377ec14457 ("genirq: Clarify documentation for request_threaded_irq()")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

With CONFIG_IRQ_FORCED_THREADING=y, testing the boolean force_irqthreads
could incur a cache line miss in invoke_softirq() and other places.

Replace the test with a static key to avoid the potential cache miss.

[ tglx: Dropped the IDE part, removed the export and updated blk-mq ]

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Tanner Love <tannerlove@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210602180338.3324213-1-tannerlove.kernel@gmail.com

Clarify wording and document commonly used IRQF_ONESHOT flag.

Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210731050740.444454-1-jsavitz@redhat.com

Merge the export of irq_set_affinity() which is a standalone commit so it
can be pulled into other trees.

Perf modules abuse irq_set_affinity_hint() to set the affinity of system
PMU interrupts just because irq_set_affinity() was not exported.

The fact that irq_set_affinity_hint() actually sets the affinity is a
non-documented side effect and the name is clearly saying it's a hint.

To clean this up, export the real affinity setter.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20210518093117.968251441@linutronix.de

The whole call to note_interrupt() can be avoided or return early when
interrupts would be marked accordingly. For IPI handlers which always
return HANDLED the whole procedure is pretty pointless to begin with.

Add a IRQF_NO_DEBUG flag and mark the interrupt accordingly if supplied
when the interrupt is requested.

When noirqdebug is set on the kernel commandline, then the interrupt is
marked unconditionally so that there is only one condition in the hotpath
to evaluate.

 [ clg: Add changelog ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/7a8ad02f-63a8-c1aa-fdd1-39d973593d02@kaod.org

Pull irq updates from Thomas Gleixner:
 "The usual updates from the irq departement:

  Core changes:

   - Provide IRQF_NO_AUTOEN as a flag for request*_irq() so drivers can
     be cleaned up which either use a seperate mechanism to prevent
     auto-enable at request time or have a racy mechanism which disables
     the interrupt right after request.

   - Get rid of the last usage of irq_create_identity_mapping() and
     remove the interface.

   - An overhaul of tasklet_disable().

     Most usage sites of tasklet_disable() are in task context and
     usually in cleanup, teardown code pathes. tasklet_disable()
     spinwaits for a tasklet which is currently executed. That's not
     only a problem for PREEMPT_RT where this can lead to a live lock
     when the disabling task preempts the softirq thread. It's also
     problematic in context of virtualization when the vCPU which runs
     the tasklet is scheduled out and the disabling code has to spin
     wait until it's scheduled back in.

     There are a few code pathes which invoke tasklet_disable() from
     non-sleepable context. For these a new disable variant which still
     spinwaits is provided which allows to switch tasklet_disable() to a
     sleep wait mechanism. For the atomic use cases this does not solve
     the live lock issue on PREEMPT_RT. That is mitigated by blocking on
     the RT specific softirq lock.

   - The PREEMPT_RT specific implementation of softirq processing and
     local_bh_disable/enable().

     On RT enabled kernels soft interrupt processing happens always in
     task context and all interrupt handlers, which are not explicitly
     marked to be invoked in hard interrupt context are forced into task
     context as well. This allows to protect against softirq processing
     with a per CPU lock, which in turn allows to make BH disabled
     regions preemptible.

     Most of the softirq handling code is still shared. The RT/non-RT
     specific differences are addressed with a set of inline functions
     which provide the context specific functionality. The
     local_bh_disable() / local_bh_enable() mechanism are obviously
     seperate.

   - The usual set of small improvements and cleanups

  Driver changes:

   - New drivers for Nuvoton WPCM450 and DT 79rc3243x interrupt
     controllers

   - Extended functionality for MStar, STM32 and SC7280 irq chips

   - Enhanced robustness for ARM GICv3/4.1 drivers

   - The usual set of cleanups and improvements all over the place"

* tag 'irq-core-2021-04-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (53 commits)
  irqchip/xilinx: Expose Kconfig option for Zynq/ZynqMP
  irqchip/gic-v3: Do not enable irqs when handling spurious interrups
  dt-bindings: interrupt-controller: Add IDT 79RC3243x Interrupt Controller
  irqchip: Add support for IDT 79rc3243x interrupt controller
  irqdomain: Drop references to recusive irqdomain setup
  irqdomain: Get rid of irq_create_strict_mappings()
  irqchip/jcore-aic: Kill use of irq_create_strict_mappings()
  ARM: PXA: Kill use of irq_create_strict_mappings()
  irqchip/gic-v4.1: Disable vSGI upon (GIC CPUIF < v4.1) detection
  irqchip/tb10x: Use 'fallthrough' to eliminate a warning
  genirq: Reduce irqdebug cacheline bouncing
  kernel: Initialize cpumask before parsing
  irqchip/wpcm450: Drop COMPILE_TEST
  irqchip/irq-mst: Support polarity configuration
  irqchip: Add driver for WPCM450 interrupt controller
  dt-bindings: interrupt-controller: Add nuvoton, wpcm450-aic
  dt-bindings: qcom,pdc: Add compatible for sc7280
  irqchip/stm32: Add usart instances exti direct event support
  irqchip/gic-v3: Fix OF_BAD_ADDR error handling
  irqchip/sifive-plic: Mark two global variables __ro_after_init
  ...

Fix ~36 single-word typos in the IRQ, irqchip and irqdomain code comments.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>