[tip: irq/core] genirq: Move prio assignment into the newly created thread

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the irq/core branch of tip:

Commit-ID:     e739f98b4b11337a4e3865364b8922a9e5ad32b6
Gitweb:        https://git.kernel.org/tip/e739f98b4b11337a4e3865364b8922a9e5ad32b6
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Tue, 10 Nov 2020 12:38:48 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 17 Sep 2021 15:08:22 +02:00

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: 710da3c8ea7df ("sched/core: Prevent race condition between cpuset and __sched_setscheduler()")
Reported-by: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
[bigeasy: Patch description]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/a23a826af7c108ea5651e73b8fbae5e653f16e86.camel@xxxxxx
---
 kernel/irq/manage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index b392483..7405e38 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -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