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ARCv2: SMP: Emulate IPI to self using software triggered interrupt

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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: Vineet Gupta <vgupta@synopsys.com>
This commit is contained in:
Vineet Gupta 2016-02-23 11:55:16 +05:30
parent 3e5177c191
commit bb143f814e
3 changed files with 32 additions and 5 deletions
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11
arch/arc/include/asm/irqflags-arcv2.h
View File

@ -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

11
arch/arc/kernel/entry-arcv2.S
View File

@ -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

15
arch/arc/kernel/mcip.c
View File

@ -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 */