Re: spinlock lockup on CPU#0

On Sat, 26 Apr 2008, Ingo Molnar wrote:
* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:

Hopefully the numbers are right, and hopefully this provides enough
info to help the kernel out

Well that's cute. At a guess I'd say that acpi_processor_idle()
managed to call sched_clock_idle_wakeup_event() with local interrupts
enabled. We took an interrupt with rq->lock held and things went
downhill from there.

Can you add this please, see if it triggers?

there's fixes pending in this area. The main fix would be the one below.

Ingo

---------------->
Subject: idle (arch, acpi and apm) and lockdep
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Fri, 25 Apr 2008 17:39:01 +0200

Oh good, thanks, I see you've just asked Linus to pull that idle fix.

Thanks to Peter for the fix, and to Justin for calling attention to it:
this freeze has been plaguing me on one x86_32 box since I put -git8
on, and I've just verified that it's the same as what's been plaguing
me on that machine since 2.6.25-mm1 came out.

Andrew, here's a belated hotfix for 2.6.25-mm1, running nicely at last:

Peter Zijlstra's "idle (arch, acpi and apm) and lockdep" fix to
recent x86 freezes - adapted to 2.6.25-mm1 by omitting merges
from process_32.c and process_64.c into process.c.

Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>
---

arch/x86/kernel/apm_32.c | 3 +++
arch/x86/kernel/process_32.c | 27 +++++++++++++++------------
arch/x86/kernel/process_64.c | 8 +++-----
drivers/acpi/processor_idle.c | 19 +++++++++----------
include/asm-x86/processor.h | 1 +
5 files changed, 31 insertions(+), 27 deletions(-)

--- 2.6.25-mm1/arch/x86/kernel/apm_32.c 2008-04-18 12:18:09.000000000 +0100
+++ linux/arch/x86/kernel/apm_32.c 2008-04-26 22:17:06.000000000 +0100
@@ -904,6 +904,7 @@ recalc:
original_pm_idle();
else
default_idle();
+ local_irq_disable();
jiffies_since_last_check = jiffies - last_jiffies;
if (jiffies_since_last_check > idle_period)
goto recalc;
@@ -911,6 +912,8 @@ recalc:

if (apm_idle_done)
apm_do_busy();
+
+ local_irq_enable();
}

/**
--- 2.6.25-mm1/arch/x86/kernel/process_32.c 2008-04-18 12:18:09.000000000 +0100
+++ linux/arch/x86/kernel/process_32.c 2008-04-26 22:29:36.000000000 +0100
@@ -111,12 +111,10 @@ void default_idle(void)
*/
smp_mb();

- local_irq_disable();
- if (!need_resched()) {
+ if (!need_resched())
safe_halt(); /* enables interrupts racelessly */
- local_irq_disable();
- }
- local_irq_enable();
+ else
+ local_irq_enable();
current_thread_info()->status |= TS_POLLING;
} else {
local_irq_enable();
@@ -196,6 +194,7 @@ void cpu_idle(void)
if (cpu_is_offline(cpu))
play_dead();

+ local_irq_disable();
__get_cpu_var(irq_stat).idle_timestamp = jiffies;
/* Don't trace irqs off for idle */
stop_critical_timings();
@@ -245,18 +244,22 @@ void mwait_idle_with_hints(unsigned long
__monitor((void *)&current_thread_info()->flags, 0, 0);
smp_mb();
if (!need_resched())
- __sti_mwait(ax, cx);
- else
- local_irq_enable();
- } else
- local_irq_enable();
+ __mwait(ax, cx);
+ }
}

/* Default MONITOR/MWAIT with no hints, used for default C1 state */
static void mwait_idle(void)
{
- local_irq_enable();
- mwait_idle_with_hints(0, 0);
+ if (!need_resched()) {
+ __monitor((void *)&current_thread_info()->flags, 0, 0);
+ smp_mb();
+ if (!need_resched())
+ __sti_mwait(0, 0);
+ else
+ local_irq_enable();
+ } else
+ local_irq_enable();
}

static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
--- 2.6.25-mm1/arch/x86/kernel/process_64.c 2008-04-18 12:18:09.000000000 +0100
+++ linux/arch/x86/kernel/process_64.c 2008-04-26 22:19:29.000000000 +0100
@@ -106,12 +106,10 @@ void default_idle(void)
* test NEED_RESCHED:
*/
smp_mb();
- local_irq_disable();
- if (!need_resched()) {
+ if (!need_resched())
safe_halt(); /* enables interrupts racelessly */
- local_irq_disable();
- }
- local_irq_enable();
+ else
+ local_irq_enable();
current_thread_info()->status |= TS_POLLING;
}

--- 2.6.25-mm1/drivers/acpi/processor_idle.c 2008-04-18 12:18:10.000000000 +0100
+++ linux/drivers/acpi/processor_idle.c 2008-04-26 22:17:06.000000000 +0100
@@ -436,13 +436,12 @@ static void acpi_processor_idle(void)

cx = pr->power.state;
if (!cx || acpi_idle_suspend) {
- if (pm_idle_save)
- pm_idle_save();
- else
+ if (pm_idle_save) {
+ pm_idle_save(); /* enables IRQs */
+ } else {
acpi_safe_halt();
-
- if (irqs_disabled())
local_irq_enable();
+ }

return;
}
@@ -538,10 +537,12 @@ static void acpi_processor_idle(void)
* Use the appropriate idle routine, the one that would
* be used without acpi C-states.
*/
- if (pm_idle_save)
- pm_idle_save();
- else
+ if (pm_idle_save) {
+ pm_idle_save(); /* enables IRQs */
+ } else {
acpi_safe_halt();
+ local_irq_enable();
+ }

/*
* TBD: Can't get time duration while in C1, as resumes
@@ -552,8 +553,6 @@ static void acpi_processor_idle(void)
* skew otherwise.
*/
sleep_ticks = 0xFFFFFFFF;
- if (irqs_disabled())
- local_irq_enable();

break;

--- 2.6.25-mm1/include/asm-x86/processor.h 2008-04-18 12:18:34.000000000 +0100
+++ linux/include/asm-x86/processor.h 2008-04-26 22:17:06.000000000 +0100
@@ -726,6 +726,7 @@ static inline void __mwait(unsigned long

static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
{
+ trace_hardirqs_on();
/* "mwait %eax, %ecx;" */
asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
:: "a" (eax), "c" (ecx));
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