linux-kernel - [PATCH 3.18 136/151] clocksource: mtk: Fix race conditions in probe code

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Message-Id: <20150304055519.752902207@linuxfoundation.org>
Date:	Tue,  3 Mar 2015 22:14:30 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Gongbae Park <yongbae2@...il.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: [PATCH 3.18 136/151] clocksource: mtk: Fix race conditions in probe code

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthias Brugger <matthias.bgg@...il.com>

commit d4a19eb3b15a4ba98f627182f48d5bc0cffae670 upstream.

We have two race conditions in the probe code which could lead to a null
pointer dereference in the interrupt handler.

The interrupt handler accesses the clockevent device, which may not yet be
registered.

First race condition happens when the interrupt handler gets registered before
the interrupts get disabled. The second race condition happens when the
interrupts get enabled, but the clockevent device is not yet registered.

Fix that by disabling the interrupts before we register the interrupt and enable
the interrupts after the clockevent device got registered.

Reported-by: Gongbae Park <yongbae2@...il.com>
Signed-off-by: Matthias Brugger <matthias.bgg@...il.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/clocksource/mtk_timer.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/clocksource/mtk_timer.c
+++ b/drivers/clocksource/mtk_timer.c
@@ -224,6 +224,8 @@ static void __init mtk_timer_init(struct
 	}
 	rate = clk_get_rate(clk);
 
+	mtk_timer_global_reset(evt);
+
 	if (request_irq(evt->dev.irq, mtk_timer_interrupt,
 			IRQF_TIMER | IRQF_IRQPOLL, "mtk_timer", evt)) {
 		pr_warn("failed to setup irq %d\n", evt->dev.irq);
@@ -232,8 +234,6 @@ static void __init mtk_timer_init(struct
 
 	evt->ticks_per_jiffy = DIV_ROUND_UP(rate, HZ);
 
-	mtk_timer_global_reset(evt);
-
 	/* Configure clock source */
 	mtk_timer_setup(evt, GPT_CLK_SRC, TIMER_CTRL_OP_FREERUN);
 	clocksource_mmio_init(evt->gpt_base + TIMER_CNT_REG(GPT_CLK_SRC),
@@ -241,10 +241,11 @@ static void __init mtk_timer_init(struct
 
 	/* Configure clock event */
 	mtk_timer_setup(evt, GPT_CLK_EVT, TIMER_CTRL_OP_REPEAT);
-	mtk_timer_enable_irq(evt, GPT_CLK_EVT);
-
 	clockevents_config_and_register(&evt->dev, rate, 0x3,
 					0xffffffff);
+
+	mtk_timer_enable_irq(evt, GPT_CLK_EVT);
+
 	return;
 
 err_clk_disable:


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