Patch "clocksource: exynos_mct: Avoid blocking calls in the cpu hotplug notifier" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

clocksource: exynos_mct: Avoid blocking calls in the cpu hotplug notifier

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
clocksource-exynos_mct-avoid-blocking-calls-in-the-cpu-hotplug-notifier.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Damian Eppel <[email protected]>
Date: Fri, 26 Jun 2015 15:23:04 +0200
Subject: clocksource: exynos_mct: Avoid blocking calls in the cpu hotplug notifier

From: Damian Eppel <[email protected]>

commit 56a94f13919c0db5958611b388e1581b4852f3c9 upstream.

Whilst testing cpu hotplug events on kernel configured with DEBUG_PREEMPT and DEBUG_ATOMIC_SLEEP we get following BUG message, caused by calling request_irq() and free_irq() in the context of hotplug notification (which is in this case atomic context).

[   40.785859] CPU1: Software reset
[   40.786660] BUG: sleeping function called from invalid context at mm/slub.c:1241
[   40.786668] in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/1
[   40.786678] Preemption disabled at:[<  (null)>]   (null)
[   40.786681]
[   40.786692] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.19.0-rc4-00024-g7dca860 #36
[   40.786698] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[   40.786728] [<c0014a00>] (unwind_backtrace) from [<c0011980>] (show_stack+0x10/0x14)
[   40.786747] [<c0011980>] (show_stack) from [<c0449ba0>] (dump_stack+0x70/0xbc)
[   40.786767] [<c0449ba0>] (dump_stack) from [<c00c6124>] (kmem_cache_alloc+0xd8/0x170)
[   40.786785] [<c00c6124>] (kmem_cache_alloc) from [<c005d6f8>] (request_threaded_irq+0x64/0x128)
[   40.786804] [<c005d6f8>] (request_threaded_irq) from [<c0350b8c>] (exynos4_local_timer_setup+0xc0/0x13c)
[   40.786820] [<c0350b8c>] (exynos4_local_timer_setup) from [<c0350ca8>] (exynos4_mct_cpu_notify+0x30/0xa8)
[   40.786838] [<c0350ca8>] (exynos4_mct_cpu_notify) from [<c003b330>] (notifier_call_chain+0x44/0x84)
[   40.786857] [<c003b330>] (notifier_call_chain) from [<c0022fd4>] (__cpu_notify+0x28/0x44)
[   40.786873] [<c0022fd4>] (__cpu_notify) from [<c0013714>] (secondary_start_kernel+0xec/0x150)
[   40.786886] [<c0013714>] (secondary_start_kernel) from [<40008764>] (0x40008764)

Interrupts cannot be requested/freed in the CPU_STARTING/CPU_DYING notifications which run on the hotplugged cpu with interrupts and preemption disabled.

To avoid the issue, request the interrupts for all possible cpus in the boot code. The interrupts are marked NO_AUTOENABLE to avoid a racy request_irq/disable_irq() sequence. The flag prevents the request_irq() code from enabling the interrupt immediately.

The interrupt is then enabled in the CPU_STARTING notifier of the hotplugged cpu and again disabled with disable_irq_nosync() in the CPU_DYING notifier.

[ tglx: Massaged changelog to match the patch ]

---
 drivers/clocksource/exynos_mct.c |   43 +++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 13 deletions(-)

@@ -422,15 +422,12 @@ static int exynos4_local_timer_setup(str
 	exynos4_mct_write(TICK_BASE_CNT, mevt->base + MCT_L_TCNTB_OFFSET);
 
 	if (mct_int_type == MCT_INT_SPI) {
-		evt->irq = mct_irqs[MCT_L0_IRQ + cpu];
-		if (request_irq(evt->irq, exynos4_mct_tick_isr,
-				IRQF_TIMER | IRQF_NOBALANCING,
-				evt->name, mevt)) {
-			pr_err("exynos-mct: cannot register IRQ %d\n",
-				evt->irq);
+
+		if (evt->irq == -1)
 			return -EIO;
-		}
-		irq_force_affinity(mct_irqs[MCT_L0_IRQ + cpu], cpumask_of(cpu));
+
+		irq_force_affinity(evt->irq, cpumask_of(cpu));
+		enable_irq(evt->irq);
 	} else {
 		enable_percpu_irq(mct_irqs[MCT_L0_IRQ], 0);
 	}

@@ -443,10 +440,12 @@ static int exynos4_local_timer_setup(str
 static void exynos4_local_timer_stop(struct clock_event_device *evt)
 {
 	evt->set_mode(CLOCK_EVT_MODE_UNUSED, evt);
-	if (mct_int_type == MCT_INT_SPI)
-		free_irq(evt->irq, this_cpu_ptr(&percpu_mct_tick));
-	else
+	if (mct_int_type == MCT_INT_SPI) {
+		if (evt->irq != -1)
+			disable_irq_nosync(evt->irq);
+	} else {
 		disable_percpu_irq(mct_irqs[MCT_L0_IRQ]);
+	}
 }
 
 static int exynos4_mct_cpu_notify(struct notifier_block *self,

@@ -478,7 +477,7 @@ static struct notifier_block exynos4_mct
 
 static void __init exynos4_timer_resources(struct device_node *np, void __iomem *base)
 {
-	int err;
+	int err, cpu;
 	struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
 	struct clk *mct_clk, *tick_clk;
 

@@ -505,7 +504,25 @@ static void __init exynos4_timer_resourc
 		WARN(err, "MCT: can't request IRQ %d (%d)\n",
 		     mct_irqs[MCT_L0_IRQ], err);
 	} else {
-		irq_set_affinity(mct_irqs[MCT_L0_IRQ], cpumask_of(0));
+		for_each_possible_cpu(cpu) {
+			int mct_irq = mct_irqs[MCT_L0_IRQ + cpu];
+			struct mct_clock_event_device *pcpu_mevt =
+				per_cpu_ptr(&percpu_mct_tick, cpu);
+
+			pcpu_mevt->evt.irq = -1;
+
+			irq_set_status_flags(mct_irq, IRQ_NOAUTOEN);
+			if (request_irq(mct_irq,
+					exynos4_mct_tick_isr,
+					IRQF_TIMER | IRQF_NOBALANCING,
+					pcpu_mevt->name, pcpu_mevt)) {
+				pr_err("exynos-mct: cannot register IRQ (cpu%d)\n",
+									cpu);
+
+				continue;
+			}
+			pcpu_mevt->evt.irq = mct_irq;
+		}
 	}
 
 	err = register_cpu_notifier(&exynos4_mct_cpu_nb);

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/clocksource-exynos_mct-avoid-blocking-calls-in-the-cpu-hotplug-notifier.patch