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Commit bb143f81 authored by Vineet Gupta's avatar Vineet Gupta
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ARCv2: SMP: Emulate IPI to self using software triggered interrupt 



ARConnect/MCIP Inter-Core-Interrupt module can't send interrupt to
local core. So use core intc capability to trigger software
interrupt to self, using an unsued IRQ #21.

This showed up as csd deadlock with LTP trace_sched on a dual core
system. This test acts as scheduler fuzzer, triggering all sorts of
schedulting activity. Trouble starts with IPI to self, which doesn't get
delivered (effectively lost due to H/w capability), but the msg intended
to be sent remain enqueued in per-cpu @ipi_data.

All subsequent IPIs to this core from other cores get elided due to the
IPI coalescing optimization in ipi_send_msg_one() where a pending msg
implies an IPI already sent and assumes other core is yet to ack it.
After the elided IPI, other core simply goes into csd_lock_wait()
but never comes out as this core never sees the interrupt.

Fixes STAR 9001008624

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>        [4.2]
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent 3e5177c1

arch/arc/include/asm/irqflags-arcv2.h

+11 −0
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#define AUX_IRQ_CTRL		0x00E

#define AUX_IRQ_ACT		0x043	/* Active Intr across all levels */

#define AUX_IRQ_LVL_PEND	0x200	/* Pending Intr across all levels */

#define AUX_IRQ_HINT		0x201	/* For generating Soft Interrupts */

#define AUX_IRQ_PRIORITY	0x206

#define ICAUSE			0x40a

#define AUX_IRQ_SELECT		0x40b
@@ -115,6 +116,16 @@ static inline int arch_irqs_disabled(void) 
	return arch_irqs_disabled_flags(arch_local_save_flags());

}



static inline void arc_softirq_trigger(int irq)

{

	write_aux_reg(AUX_IRQ_HINT, irq);

}



static inline void arc_softirq_clear(int irq)

{

	write_aux_reg(AUX_IRQ_HINT, 0);

}



#else



.macro IRQ_DISABLE  scratch

arch/arc/kernel/entry-arcv2.S

+6 −5
Original line number Diff line number Diff line
@@ -45,11 +45,12 @@ VECTOR reserved ; Reserved slots 
VECTOR	handle_interrupt	; (16) Timer0

VECTOR	handle_interrupt	; unused (Timer1)

VECTOR	handle_interrupt	; unused (WDT)

VECTOR	handle_interrupt	; (19) ICI (inter core interrupt)

VECTOR	handle_interrupt

VECTOR	handle_interrupt

VECTOR	handle_interrupt

VECTOR	handle_interrupt	; (23) End of fixed IRQs

VECTOR	handle_interrupt	; (19) Inter core Interrupt (IPI)

VECTOR	handle_interrupt	; (20) perf Interrupt

VECTOR	handle_interrupt	; (21) Software Triggered Intr (Self IPI)

VECTOR	handle_interrupt	; unused

VECTOR	handle_interrupt	; (23) unused

# End of fixed IRQs



.rept CONFIG_ARC_NUMBER_OF_INTERRUPTS - 8

	VECTOR	handle_interrupt

arch/arc/kernel/mcip.c

+15 −0
Original line number Diff line number Diff line
@@ -11,9 +11,12 @@ 
#include <linux/smp.h>

#include <linux/irq.h>

#include <linux/spinlock.h>

#include <asm/irqflags-arcv2.h>

#include <asm/mcip.h>

#include <asm/setup.h>



#define SOFTIRQ_IRQ	21



static char smp_cpuinfo_buf[128];

static int idu_detected;
@@ -22,6 +25,7 @@ static DEFINE_RAW_SPINLOCK(mcip_lock); 
static void mcip_setup_per_cpu(int cpu)

{

	smp_ipi_irq_setup(cpu, IPI_IRQ);

	smp_ipi_irq_setup(cpu, SOFTIRQ_IRQ);

}



static void mcip_ipi_send(int cpu)
@@ -29,6 +33,12 @@ static void mcip_ipi_send(int cpu) 
	unsigned long flags;

	int ipi_was_pending;



	/* ARConnect can only send IPI to others */

	if (unlikely(cpu == raw_smp_processor_id())) {

		arc_softirq_trigger(SOFTIRQ_IRQ);

		return;

	}



	/*

	 * NOTE: We must spin here if the other cpu hasn't yet

	 * serviced a previous message. This can burn lots
@@ -63,6 +73,11 @@ static void mcip_ipi_clear(int irq) 
	unsigned long flags;

	unsigned int __maybe_unused copy;



	if (unlikely(irq == SOFTIRQ_IRQ)) {

		arc_softirq_clear(irq);

		return;

	}



	raw_spin_lock_irqsave(&mcip_lock, flags);



	/* Who sent the IPI */