linux-kernel - [PATCH] irqchip/irq-mtk-sysirq: drop unnecessary spinlock

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Message-Id: <20200527161743.15972-1-brgl@bgdev.pl>
Date:   Wed, 27 May 2020 18:17:43 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Fabien Parent <fparent@...libre.com>,
        Stephane Le Provost <stephane.leprovost@...iatek.com>,
        Pedro Tsai <pedro.tsai@...iatek.com>,
        Andrew Perepech <andrew.perepech@...iatek.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: [PATCH] irqchip/irq-mtk-sysirq: drop unnecessary spinlock

From: Bartosz Golaszewski <bgolaszewski@...libre.com>

This driver takes a regular spinlock when a raw spinlock is already
taken which results in the following lockdep splat:

=============================
[ BUG: Invalid wait context ]
5.7.0-rc6-02446-gb9827c0a9fe7-dirty #1 Not tainted
-----------------------------
swapper/0/0 is trying to lock:
ffffff800303b798 (&chip_data->lock){....}-{3:3}, at: mtk_sysirq_set_type+0x48/0xc0
other info that might help us debug this:
context-{5:5}
2 locks held by swapper/0/0:
 #0: ffffff800302ee68 (&desc->request_mutex){....}-{4:4}, at: __setup_irq+0xc4/0x8a0
 #1: ffffff800302ecf0 (&irq_desc_lock_class){....}-{2:2}, at: __setup_irq+0xe4/0x8a0
stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.7.0-rc6-02446-gb9827c0a9fe7-dirty #1
Hardware name: Pumpkin MT8516 (DT)
Call trace:
 dump_backtrace+0x0/0x180
 show_stack+0x14/0x20
 dump_stack+0xd0/0x118
 __lock_acquire+0x8c8/0x2270
 lock_acquire+0xf8/0x470
 _raw_spin_lock_irqsave+0x50/0x78
 mtk_sysirq_set_type+0x48/0xc0
 __irq_set_trigger+0x58/0x170
 __setup_irq+0x420/0x8a0
 request_threaded_irq+0xd8/0x190
 timer_of_init+0x1e8/0x2c4
 mtk_gpt_init+0x5c/0x1dc
 timer_probe+0x74/0xf4
 time_init+0x14/0x44
 start_kernel+0x394/0x4f0

We don't need the spinlock here - the irq_set_type() callback is always
called with the irq_desc->lock taken. This removes the spinlock entirely.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
---
 drivers/irqchip/irq-mtk-sysirq.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/irqchip/irq-mtk-sysirq.c b/drivers/irqchip/irq-mtk-sysirq.c
index 73eae5966a40..da2fc4809222 100644
--- a/drivers/irqchip/irq-mtk-sysirq.c
+++ b/drivers/irqchip/irq-mtk-sysirq.c
@@ -12,10 +12,8 @@
 #include <linux/of_address.h>
 #include <linux/io.h>
 #include <linux/slab.h>
-#include <linux/spinlock.h>
 
 struct mtk_sysirq_chip_data {
-	spinlock_t lock;
 	u32 nr_intpol_bases;
 	void __iomem **intpol_bases;
 	u32 *intpol_words;
@@ -30,14 +28,12 @@ static int mtk_sysirq_set_type(struct irq_data *data, unsigned int type)
 	u8 intpol_idx = chip_data->intpol_idx[hwirq];
 	void __iomem *base;
 	u32 offset, reg_index, value;
-	unsigned long flags;
 	int ret;
 
 	base = chip_data->intpol_bases[intpol_idx];
 	reg_index = chip_data->which_word[hwirq];
 	offset = hwirq & 0x1f;
 
-	spin_lock_irqsave(&chip_data->lock, flags);
 	value = readl_relaxed(base + reg_index * 4);
 	if (type == IRQ_TYPE_LEVEL_LOW || type == IRQ_TYPE_EDGE_FALLING) {
 		if (type == IRQ_TYPE_LEVEL_LOW)
@@ -53,7 +49,6 @@ static int mtk_sysirq_set_type(struct irq_data *data, unsigned int type)
 
 	data = data->parent_data;
 	ret = data->chip->irq_set_type(data, type);
-	spin_unlock_irqrestore(&chip_data->lock, flags);
 	return ret;
 }
 
@@ -212,7 +207,6 @@ static int __init mtk_sysirq_of_init(struct device_node *node,
 		ret = -ENOMEM;
 		goto out_free_which_word;
 	}
-	spin_lock_init(&chip_data->lock);
 
 	return 0;
 
-- 
2.25.0