Commit e739f98b authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

genirq: Move prio assignment into the newly created thread 



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: 710da3c8 ("sched/core: Prevent race condition between cpuset and __sched_setscheduler()")
Reported-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
[bigeasy: Patch description]
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/a23a826af7c108ea5651e73b8fbae5e653f16e86.camel@gmx.de
parent e1a6af4b

kernel/irq/manage.c

+2 −2
Original line number Diff line number Diff line
@@ -1259,6 +1259,8 @@ static int irq_thread(void *data) 
	irqreturn_t (*handler_fn)(struct irq_desc *desc,

			struct irqaction *action);



	sched_set_fifo(current);



	if (force_irqthreads() && test_bit(IRQTF_FORCED_THREAD,

					   &action->thread_flags))

		handler_fn = irq_forced_thread_fn;
@@ -1424,8 +1426,6 @@ setup_irq_thread(struct irqaction *new, unsigned int irq, bool secondary) 
	if (IS_ERR(t))

		return PTR_ERR(t);



	sched_set_fifo(t);



	/*

	 * We keep the reference to the task struct even if

	 * the thread dies to avoid that the interrupt code