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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-kernel@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Ben Skeggs <bskeggs@redhat.com>, Mike Galbraith <efault@gmx.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH 2/2] genirq: Move prio assignment into the newly created thread
Date: Tue, 10 Nov 2020 12:38:48 +0100	[thread overview]
Message-ID: <20201110113848.801379-3-bigeasy@linutronix.de> (raw)
In-Reply-To: <20201110113848.801379-1-bigeasy@linutronix.de>

From: Thomas Gleixner <tglx@linutronix.de>

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>
Link: https://lkml.kernel.org/r/a23a826af7c108ea5651e73b8fbae5e653f16e86.camel@gmx.de
---
 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 c460e0496006e..079688d122a70 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1155,6 +1155,8 @@ 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;
@@ -1320,8 +1322,6 @@ 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
-- 
2.29.2


      parent reply	other threads:[~2020-11-10 11:39 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-10 11:38 [PATCH 0/2] " Sebastian Andrzej Siewior
2020-11-10 11:38 ` [PATCH 1/2] kthread: Move prio/affinite change " Sebastian Andrzej Siewior
2020-11-17 12:45   ` Peter Zijlstra
2020-11-20 22:17     ` Sebastian Andrzej Siewior
2020-11-21 10:55     ` Thomas Gleixner
2021-03-03 16:25       ` Sebastian Andrzej Siewior
2020-11-10 11:38 ` Sebastian Andrzej Siewior [this message]

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