* [PATCH 1/5] ARCv2: SMP: Emulate IPI to self using software triggered interrupt
2016-02-23 9:11 [PATCH 0/5] ARC IPI related fix Vineet Gupta
@ 2016-02-23 9:11 ` Vineet Gupta
2016-02-23 9:11 ` [PATCH 2/5] ARC: [intc-compact] Remove IPI setup from ARCompact port Vineet Gupta
` (3 subsequent siblings)
4 siblings, 0 replies; 7+ messages in thread
From: Vineet Gupta @ 2016-02-23 9:11 UTC (permalink / raw)
To: linux-snps-arc
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 at infradead.org>
Cc: <stable at vger.kernel.org> [4.2]
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
---
arch/arc/include/asm/irqflags-arcv2.h | 11 +++++++++++
arch/arc/kernel/mcip.c | 15 +++++++++++++++
2 files changed, 26 insertions(+)
diff --git a/arch/arc/include/asm/irqflags-arcv2.h b/arch/arc/include/asm/irqflags-arcv2.h
index 1fc18ee06cf2..37c2f751eebf 100644
--- a/arch/arc/include/asm/irqflags-arcv2.h
+++ b/arch/arc/include/asm/irqflags-arcv2.h
@@ -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
diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
index 002c5fcf8947..9e1bd03b87a6 100644
--- a/arch/arc/kernel/mcip.c
+++ b/arch/arc/kernel/mcip.c
@@ -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 */
--
2.5.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH 2/5] ARC: [intc-compact] Remove IPI setup from ARCompact port
2016-02-23 9:11 [PATCH 0/5] ARC IPI related fix Vineet Gupta
2016-02-23 9:11 ` [PATCH 1/5] ARCv2: SMP: Emulate IPI to self using software triggered interrupt Vineet Gupta
@ 2016-02-23 9:11 ` Vineet Gupta
2016-02-23 9:11 ` [PATCH 3/5] ARCv2: SMP: Push IPI_IRQ into IPI provider Vineet Gupta
` (2 subsequent siblings)
4 siblings, 0 replies; 7+ messages in thread
From: Vineet Gupta @ 2016-02-23 9:11 UTC (permalink / raw)
To: linux-snps-arc
There is no real ARC700 based SMP SoC so remove IPI definition.
EZChip's SMP ARC700 is going to use a different intc and IPI provider
anyways.
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
---
arch/arc/include/asm/irq.h | 1 -
arch/arc/kernel/intc-compact.c | 3 ---
2 files changed, 4 deletions(-)
diff --git a/arch/arc/include/asm/irq.h b/arch/arc/include/asm/irq.h
index 4fd7d62a6e30..bc5103637326 100644
--- a/arch/arc/include/asm/irq.h
+++ b/arch/arc/include/asm/irq.h
@@ -16,7 +16,6 @@
#ifdef CONFIG_ISA_ARCOMPACT
#define TIMER0_IRQ 3
#define TIMER1_IRQ 4
-#define IPI_IRQ (NR_CPU_IRQS-1) /* dummy to enable SMP build for up hardware */
#else
#define TIMER0_IRQ 16
#define TIMER1_IRQ 17
diff --git a/arch/arc/kernel/intc-compact.c b/arch/arc/kernel/intc-compact.c
index 06bcedf19b62..224d1c3aa9c4 100644
--- a/arch/arc/kernel/intc-compact.c
+++ b/arch/arc/kernel/intc-compact.c
@@ -81,9 +81,6 @@ static int arc_intc_domain_map(struct irq_domain *d, unsigned int irq,
{
switch (irq) {
case TIMER0_IRQ:
-#ifdef CONFIG_SMP
- case IPI_IRQ:
-#endif
irq_set_chip_and_handler(irq, &onchip_intc, handle_percpu_irq);
break;
default:
--
2.5.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH 3/5] ARCv2: SMP: Push IPI_IRQ into IPI provider
2016-02-23 9:11 [PATCH 0/5] ARC IPI related fix Vineet Gupta
2016-02-23 9:11 ` [PATCH 1/5] ARCv2: SMP: Emulate IPI to self using software triggered interrupt Vineet Gupta
2016-02-23 9:11 ` [PATCH 2/5] ARC: [intc-compact] Remove IPI setup from ARCompact port Vineet Gupta
@ 2016-02-23 9:11 ` Vineet Gupta
2016-02-23 9:11 ` [PATCH 4/5] ARCv2: Elide sending new cross core intr if receiver didn't ack prev Vineet Gupta
2016-02-23 9:11 ` [PATCH 5/5] ARC: SMP: No need for CONFIG_ARC_IPI_DBG Vineet Gupta
4 siblings, 0 replies; 7+ messages in thread
From: Vineet Gupta @ 2016-02-23 9:11 UTC (permalink / raw)
To: linux-snps-arc
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
---
arch/arc/include/asm/irq.h | 1 -
arch/arc/kernel/mcip.c | 1 +
2 files changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arc/include/asm/irq.h b/arch/arc/include/asm/irq.h
index bc5103637326..49014f0ef36d 100644
--- a/arch/arc/include/asm/irq.h
+++ b/arch/arc/include/asm/irq.h
@@ -19,7 +19,6 @@
#else
#define TIMER0_IRQ 16
#define TIMER1_IRQ 17
-#define IPI_IRQ 19
#endif
#include <linux/interrupt.h>
diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
index 9e1bd03b87a6..e30d5d428330 100644
--- a/arch/arc/kernel/mcip.c
+++ b/arch/arc/kernel/mcip.c
@@ -15,6 +15,7 @@
#include <asm/mcip.h>
#include <asm/setup.h>
+#define IPI_IRQ 19
#define SOFTIRQ_IRQ 21
static char smp_cpuinfo_buf[128];
--
2.5.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH 4/5] ARCv2: Elide sending new cross core intr if receiver didn't ack prev
2016-02-23 9:11 [PATCH 0/5] ARC IPI related fix Vineet Gupta
` (2 preceding siblings ...)
2016-02-23 9:11 ` [PATCH 3/5] ARCv2: SMP: Push IPI_IRQ into IPI provider Vineet Gupta
@ 2016-02-23 9:11 ` Vineet Gupta
2016-02-26 11:02 ` Vineet Gupta
2016-02-23 9:11 ` [PATCH 5/5] ARC: SMP: No need for CONFIG_ARC_IPI_DBG Vineet Gupta
4 siblings, 1 reply; 7+ messages in thread
From: Vineet Gupta @ 2016-02-23 9:11 UTC (permalink / raw)
To: linux-snps-arc
ARConnect/MCIP IPI sending has a retry-wait loop in case caller had
not seen a previous such interrupt. Turns out that it is not needed at
all. Linux cross core calling allows coalescing multiple IPIs to same
receiver - it is fine as long as there is one.
This logic is built into upper layer already, at a higher level of
abstraction. ipi_send_msg_one() sets the actual msg payload, but it only
calls MCIP IPI sending if msg holder was empty (using
atomic-set-new-and-get-old construct). Thus it is unlikely that the
retry-wait looping was ever getting exercised at all.
Cc: Chuck Jordan <cjordan at synopsys.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
---
arch/arc/kernel/mcip.c | 27 ++++++++++-----------------
1 file changed, 10 insertions(+), 17 deletions(-)
diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
index e30d5d428330..7afc3c703ed1 100644
--- a/arch/arc/kernel/mcip.c
+++ b/arch/arc/kernel/mcip.c
@@ -40,26 +40,19 @@ static void mcip_ipi_send(int cpu)
return;
}
+ raw_spin_lock_irqsave(&mcip_lock, flags);
+
/*
- * NOTE: We must spin here if the other cpu hasn't yet
- * serviced a previous message. This can burn lots
- * of time, but we MUST follows this protocol or
- * ipi messages can be lost!!!
- * Also, we must release the lock in this loop because
- * the other side may get to this same loop and not
- * be able to ack -- thus causing deadlock.
+ * If receiver already has a pending interrupt, elide sending this one.
+ * Linux cross core calling works well with concurrent IPIs
+ * coalesced into one
+ * see arch/arc/kernel/smp.c: ipi_send_msg_one()
*/
+ __mcip_cmd(CMD_INTRPT_READ_STATUS, cpu);
+ ipi_was_pending = read_aux_reg(ARC_REG_MCIP_READBACK);
+ if (!ipi_was_pending)
+ __mcip_cmd(CMD_INTRPT_GENERATE_IRQ, cpu);
- do {
- raw_spin_lock_irqsave(&mcip_lock, flags);
- __mcip_cmd(CMD_INTRPT_READ_STATUS, cpu);
- ipi_was_pending = read_aux_reg(ARC_REG_MCIP_READBACK);
- if (ipi_was_pending == 0)
- break; /* break out but keep lock */
- raw_spin_unlock_irqrestore(&mcip_lock, flags);
- } while (1);
-
- __mcip_cmd(CMD_INTRPT_GENERATE_IRQ, cpu);
raw_spin_unlock_irqrestore(&mcip_lock, flags);
#ifdef CONFIG_ARC_IPI_DBG
--
2.5.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH 4/5] ARCv2: Elide sending new cross core intr if receiver didn't ack prev
2016-02-23 9:11 ` [PATCH 4/5] ARCv2: Elide sending new cross core intr if receiver didn't ack prev Vineet Gupta
@ 2016-02-26 11:02 ` Vineet Gupta
0 siblings, 0 replies; 7+ messages in thread
From: Vineet Gupta @ 2016-02-26 11:02 UTC (permalink / raw)
To: linux-snps-arc
On Tuesday 23 February 2016 02:41 PM, Vineet Gupta wrote:
> ARConnect/MCIP IPI sending has a retry-wait loop in case caller had
> not seen a previous such interrupt. Turns out that it is not needed at
> all. Linux cross core calling allows coalescing multiple IPIs to same
> receiver - it is fine as long as there is one.
>
> This logic is built into upper layer already, at a higher level of
> abstraction. ipi_send_msg_one() sets the actual msg payload, but it only
> calls MCIP IPI sending if msg holder was empty (using
> atomic-set-new-and-get-old construct). Thus it is unlikely that the
> retry-wait looping was ever getting exercised at all.
Turns out that this patch was needed for more serious reasons.
For experiment sake I reverted the IPI eliding optimization and immediately ran
into a deadlock, with LTP:trace_sched !
@@ -241,7 +241,7 @@ static void ipi_send_msg_one(int cpu, enum ipi_msg_type msg)
* IPI handler, because !@old means it has not yet dequeued the msg(s)
* so @new msg can be a free-loader
*/
- if (plat_smp_ops.ipi_send && !old)
+ if (plat_smp_ops.ipi_send)
-Vineet
>
> Cc: Chuck Jordan <cjordan at synopsys.com>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
> ---
> arch/arc/kernel/mcip.c | 27 ++++++++++-----------------
> 1 file changed, 10 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
> index e30d5d428330..7afc3c703ed1 100644
> --- a/arch/arc/kernel/mcip.c
> +++ b/arch/arc/kernel/mcip.c
> @@ -40,26 +40,19 @@ static void mcip_ipi_send(int cpu)
> return;
> }
>
> + raw_spin_lock_irqsave(&mcip_lock, flags);
> +
> /*
> - * NOTE: We must spin here if the other cpu hasn't yet
> - * serviced a previous message. This can burn lots
> - * of time, but we MUST follows this protocol or
> - * ipi messages can be lost!!!
> - * Also, we must release the lock in this loop because
> - * the other side may get to this same loop and not
> - * be able to ack -- thus causing deadlock.
> + * If receiver already has a pending interrupt, elide sending this one.
> + * Linux cross core calling works well with concurrent IPIs
> + * coalesced into one
> + * see arch/arc/kernel/smp.c: ipi_send_msg_one()
> */
> + __mcip_cmd(CMD_INTRPT_READ_STATUS, cpu);
> + ipi_was_pending = read_aux_reg(ARC_REG_MCIP_READBACK);
> + if (!ipi_was_pending)
> + __mcip_cmd(CMD_INTRPT_GENERATE_IRQ, cpu);
>
> - do {
> - raw_spin_lock_irqsave(&mcip_lock, flags);
> - __mcip_cmd(CMD_INTRPT_READ_STATUS, cpu);
> - ipi_was_pending = read_aux_reg(ARC_REG_MCIP_READBACK);
> - if (ipi_was_pending == 0)
> - break; /* break out but keep lock */
> - raw_spin_unlock_irqrestore(&mcip_lock, flags);
> - } while (1);
> -
> - __mcip_cmd(CMD_INTRPT_GENERATE_IRQ, cpu);
> raw_spin_unlock_irqrestore(&mcip_lock, flags);
>
> #ifdef CONFIG_ARC_IPI_DBG
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 5/5] ARC: SMP: No need for CONFIG_ARC_IPI_DBG
2016-02-23 9:11 [PATCH 0/5] ARC IPI related fix Vineet Gupta
` (3 preceding siblings ...)
2016-02-23 9:11 ` [PATCH 4/5] ARCv2: Elide sending new cross core intr if receiver didn't ack prev Vineet Gupta
@ 2016-02-23 9:11 ` Vineet Gupta
4 siblings, 0 replies; 7+ messages in thread
From: Vineet Gupta @ 2016-02-23 9:11 UTC (permalink / raw)
To: linux-snps-arc
This was more relevant during SMP bringup.
The warning for bogus msg better be visible always.
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
---
arch/arc/Kconfig | 8 --------
arch/arc/kernel/mcip.c | 9 +--------
arch/arc/kernel/smp.c | 3 ---
3 files changed, 1 insertion(+), 19 deletions(-)
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 4abc81907071..8a188bc1786a 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -532,14 +532,6 @@ config ARC_DBG_TLB_MISS_COUNT
Counts number of I and D TLB Misses and exports them via Debugfs
The counters can be cleared via Debugfs as well
-if SMP
-
-config ARC_IPI_DBG
- bool "Debug Inter Core interrupts"
- default n
-
-endif
-
endif
config ARC_UBOOT_SUPPORT
diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
index 7afc3c703ed1..7b4af70ffd18 100644
--- a/arch/arc/kernel/mcip.c
+++ b/arch/arc/kernel/mcip.c
@@ -65,7 +65,6 @@ static void mcip_ipi_clear(int irq)
{
unsigned int cpu, c;
unsigned long flags;
- unsigned int __maybe_unused copy;
if (unlikely(irq == SOFTIRQ_IRQ)) {
arc_softirq_clear(irq);
@@ -77,7 +76,7 @@ static void mcip_ipi_clear(int irq)
/* Who sent the IPI */
__mcip_cmd(CMD_INTRPT_CHECK_SOURCE, 0);
- copy = cpu = read_aux_reg(ARC_REG_MCIP_READBACK); /* 1,2,4,8... */
+ cpu = read_aux_reg(ARC_REG_MCIP_READBACK); /* 1,2,4,8... */
/*
* In rare case, multiple concurrent IPIs sent to same target can
@@ -91,12 +90,6 @@ static void mcip_ipi_clear(int irq)
} while (cpu);
raw_spin_unlock_irqrestore(&mcip_lock, flags);
-
-#ifdef CONFIG_ARC_IPI_DBG
- if (c != __ffs(copy))
- pr_info("IPIs from %x coalesced to %x\n",
- copy, raw_smp_processor_id());
-#endif
}
static void mcip_probe_n_setup(void)
diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index ef6e9e15b82a..424e937da5c8 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -336,11 +336,8 @@ irqreturn_t do_IPI(int irq, void *dev_id)
int rc;
rc = __do_IPI(msg);
-#ifdef CONFIG_ARC_IPI_DBG
- /* IPI received but no valid @msg */
if (rc)
pr_info("IPI with bogus msg %ld in %ld\n", msg, copy);
-#endif
pending &= ~(1U << msg);
} while (pending);
--
2.5.0
^ permalink raw reply related [flat|nested] 7+ messages in thread