[PATCH] [RFC] PowerPC64: Use preempt_schedule_irq instead of preempt_schedule when returning from exceptions

[PATCH] [RFC] PowerPC64: Use preempt_schedule_irq instead of preempt_schedule when returning from exceptions

[Valentine Barshak]

Use preempt_schedule_irq to prevent infinite irq-entry and
eventual stack overflow problems with fast-paced IRQ sources.
This kind of problems has been observed on the PASemi Electra IDE
controller. We have to make sure we are soft-disabled before calling
preempt_schedule_irq and hard disable interrupts after that
to avoid unrecoverable exceptions.

This patch also moves the "clrrdi r9,r1,THREAD_SHIFT" out of
the #ifdef CONFIG_PPC_BOOK3E scope, since r9 is clobbered
and has to be restored in both cases.

Signed-off-by: Valentine Barshak <vbarshak@ru.mvista.com>
---
 arch/powerpc/kernel/entry_64.S |   25 ++++++-------------------
 1 file changed, 6 insertions(+), 19 deletions(-)

diff -pruN linux-2.6.orig/arch/powerpc/kernel/entry_64.S linux-2.6.new/arch/powerpc/kernel/entry_64.S
--- linux-2.6.orig/arch/powerpc/kernel/entry_64.S	2009-10-17 03:46:26.000000000 +0400
+++ linux-2.6.new/arch/powerpc/kernel/entry_64.S	2009-10-19 17:35:16.000000000 +0400
@@ -660,33 +660,20 @@ do_work:
 	bne	restore
 	/* here we are preempting the current task */
 1:
-#ifdef CONFIG_TRACE_IRQFLAGS
-	bl	.trace_hardirqs_on
-	/* Note: we just clobbered r10 which used to contain the previous
-	 * MSR before the hard-disabling done by the caller of do_work.
-	 * We don't have that value anymore, but it doesn't matter as
-	 * we will hard-enable unconditionally, we can just reload the
-	 * current MSR into r10
-	 */
-	mfmsr	r10
-#endif /* CONFIG_TRACE_IRQFLAGS */
-	li	r0,1
+	/* ensure we are soft-disabled */
+	li	r0,0
 	stb	r0,PACASOFTIRQEN(r13)
-	stb	r0,PACAHARDIRQEN(r13)
+	bl	.preempt_schedule_irq
+	/* hard-disable interrupts */
 #ifdef CONFIG_PPC_BOOK3E
-	wrteei	1
-	bl	.preempt_schedule
 	wrteei	0
 #else
-	ori	r10,r10,MSR_EE
-	mtmsrd	r10,1		/* reenable interrupts */
-	bl	.preempt_schedule
 	mfmsr	r10
-	clrrdi	r9,r1,THREAD_SHIFT
-	rldicl	r10,r10,48,1	/* disable interrupts again */
+	rldicl	r10,r10,48,1
 	rotldi	r10,r10,16
 	mtmsrd	r10,1
 #endif /* CONFIG_PPC_BOOK3E */
+	clrrdi	r9,r1,THREAD_SHIFT
 	ld	r4,TI_FLAGS(r9)
 	andi.	r0,r4,_TIF_NEED_RESCHED
 	bne	1b

Re: [PATCH] [RFC] PowerPC64: Use preempt_schedule_irq instead of preempt_schedule when returning from exceptions

[Benjamin Herrenschmidt]

On Mon, 2009-10-19 at 22:28 +0400, Valentine Barshak wrote:
> Use preempt_schedule_irq to prevent infinite irq-entry and
> eventual stack overflow problems with fast-paced IRQ sources.
> This kind of problems has been observed on the PASemi Electra IDE
> controller. We have to make sure we are soft-disabled before calling
> preempt_schedule_irq and hard disable interrupts after that
> to avoid unrecoverable exceptions.
> 
> This patch also moves the "clrrdi r9,r1,THREAD_SHIFT" out of
> the #ifdef CONFIG_PPC_BOOK3E scope, since r9 is clobbered
> and has to be restored in both cases.

So I _think_ that the irqs on/off accounting for lockdep isn't quite
right. What do you think of this slightly modified version ? I've only
done a quick boot test on a G5 with lockdep enabled and a played a bit,
nothing shows up so far but it's definitely not conclusive.

The main difference is that I call trace_hardirqs_off to "advertise"
the fact that we are soft-disabling (it could be a dup, but at this
stage this is no big deal, but it's not always, like in syscall return
the kernel thinks we have interrupts enabled and could thus get out
of sync without that).

I also mark the PACA hard disable to reflect the MSR:EE state before
calling into preempt_schedule_irq().

---

[PATCH v2] powerpc: Use preempt_schedule_irq instead of preempt_schedule when returning from exceptions

Use preempt_schedule_irq to prevent infinite irq-entry and
eventual stack overflow problems with fast-paced IRQ sources.
This kind of problems has been observed on the PASemi Electra IDE
controller. We have to make sure we are soft-disabled before calling
preempt_schedule_irq and hard disable interrupts after that
to avoid unrecoverable exceptions.

This patch also moves the "clrrdi r9,r1,THREAD_SHIFT" out of
the #ifdef CONFIG_PPC_BOOK3E scope, since r9 is clobbered
and has to be restored in both cases.

Signed-off-by: Valentine Barshak <vbarshak@ru.mvista.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 arch/powerpc/kernel/entry_64.S |   38 +++++++++++++++++++++-----------------
 1 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index f9fd54b..b64ae3d 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -659,34 +659,38 @@ do_work:
 	crandc	eq,cr1*4+eq,eq
 	bne	restore
 	/* here we are preempting the current task */
-1:
+	/* ensure we are soft-disabled
+	 * */
+	li	r0,0
+	stb	r0,PACASOFTIRQEN(r13)
+	/* Trace the IRQ state change */
 #ifdef CONFIG_TRACE_IRQFLAGS
-	bl	.trace_hardirqs_on
-	/* Note: we just clobbered r10 which used to contain the previous
-	 * MSR before the hard-disabling done by the caller of do_work.
-	 * We don't have that value anymore, but it doesn't matter as
-	 * we will hard-enable unconditionally, we can just reload the
-	 * current MSR into r10
-	 */
+	bl	.trace_hardirqs_off
+#endif
+1:	/* And make sure we are hard-enabled */
+#ifdef CONFIG_PPC_BOOK3E
+	wrteei	1
+#else
 	mfmsr	r10
-#endif /* CONFIG_TRACE_IRQFLAGS */
+	ori	r10,r10,MSR_EE
+	mtmsrd	r10,1
+#endif
 	li	r0,1
-	stb	r0,PACASOFTIRQEN(r13)
 	stb	r0,PACAHARDIRQEN(r13)
+	/* Call the scheduler with soft IRQs off */
+	bl	.preempt_schedule_irq
+	/* hard-disable interrupts again */
 #ifdef CONFIG_PPC_BOOK3E
-	wrteei	1
-	bl	.preempt_schedule
 	wrteei	0
 #else
-	ori	r10,r10,MSR_EE
-	mtmsrd	r10,1		/* reenable interrupts */
-	bl	.preempt_schedule
 	mfmsr	r10
-	clrrdi	r9,r1,THREAD_SHIFT
-	rldicl	r10,r10,48,1	/* disable interrupts again */
+	rldicl	r10,r10,48,1
 	rotldi	r10,r10,16
 	mtmsrd	r10,1
 #endif /* CONFIG_PPC_BOOK3E */
+	li	r0,0
+	stb	r0,PACAHARDIRQEN(r13)
+	clrrdi	r9,r1,THREAD_SHIFT
 	ld	r4,TI_FLAGS(r9)
 	andi.	r0,r4,_TIF_NEED_RESCHED
 	bne	1b
-- 
1.6.1.2.14.gf26b5

[PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Benjamin Herrenschmidt]

> So I _think_ that the irqs on/off accounting for lockdep isn't quite
> right. What do you think of this slightly modified version ? I've only
> done a quick boot test on a G5 with lockdep enabled and a played a bit,
> nothing shows up so far but it's definitely not conclusive.
> 
> The main difference is that I call trace_hardirqs_off to "advertise"
> the fact that we are soft-disabling (it could be a dup, but at this
> stage this is no big deal, but it's not always, like in syscall return
> the kernel thinks we have interrupts enabled and could thus get out
> of sync without that).
> 
> I also mark the PACA hard disable to reflect the MSR:EE state before
> calling into preempt_schedule_irq().

Allright, second thought :-)

It's probably simpler to just keep hardirqs off. Code is smaller and
simpler and the scheduler will re-enable them soon enough anyways.

This version of the patch also spaces the code a bit and adds comments
which makes them (the code and the patch) more readable.

Cheers,
Ben.
 
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

[PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

Based on an original patch by Valentine Barshak <vbarshak@ru.mvista.com>

Use preempt_schedule_irq to prevent infinite irq-entry and
eventual stack overflow problems with fast-paced IRQ sources.

This kind of problems has been observed on the PASemi Electra IDE
controller. We have to make sure we are soft-disabled before calling
preempt_schedule_irq and hard disable interrupts after that
to avoid unrecoverable exceptions.

This patch also moves the "clrrdi r9,r1,THREAD_SHIFT" out of
the #ifdef CONFIG_PPC_BOOK3E scope, since r9 is clobbered
and has to be restored in both cases.
---
 arch/powerpc/kernel/entry_64.S |   41 ++++++++++++++++++++-------------------
 1 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index f9fd54b..9763267 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -658,42 +658,43 @@ do_work:
 	cmpdi	r0,0
 	crandc	eq,cr1*4+eq,eq
 	bne	restore
-	/* here we are preempting the current task */
-1:
-#ifdef CONFIG_TRACE_IRQFLAGS
-	bl	.trace_hardirqs_on
-	/* Note: we just clobbered r10 which used to contain the previous
-	 * MSR before the hard-disabling done by the caller of do_work.
-	 * We don't have that value anymore, but it doesn't matter as
-	 * we will hard-enable unconditionally, we can just reload the
-	 * current MSR into r10
+
+	/* Here we are preempting the current task.
+	 *
+	 * Ensure interrupts are soft-disabled. We also properly mark
+	 * the PACA to reflect the fact that they are hard-disabled
+	 * and trace the change
 	 */
-	mfmsr	r10
-#endif /* CONFIG_TRACE_IRQFLAGS */
-	li	r0,1
+	li	r0,0
 	stb	r0,PACASOFTIRQEN(r13)
 	stb	r0,PACAHARDIRQEN(r13)
+	TRACE_DISABLE_INTS
+
+	/* Call the scheduler with soft IRQs off */
+1:	bl	.preempt_schedule_irq
+
+	/* Hard-disable interrupts again (and update PACA) */
 #ifdef CONFIG_PPC_BOOK3E
-	wrteei	1
-	bl	.preempt_schedule
 	wrteei	0
 #else
-	ori	r10,r10,MSR_EE
-	mtmsrd	r10,1		/* reenable interrupts */
-	bl	.preempt_schedule
 	mfmsr	r10
-	clrrdi	r9,r1,THREAD_SHIFT
-	rldicl	r10,r10,48,1	/* disable interrupts again */
+	rldicl	r10,r10,48,1
 	rotldi	r10,r10,16
 	mtmsrd	r10,1
 #endif /* CONFIG_PPC_BOOK3E */
+	li	r0,0
+	stb	r0,PACAHARDIRQEN(r13)
+
+	/* Re-test flags and eventually loop */
+	clrrdi	r9,r1,THREAD_SHIFT
 	ld	r4,TI_FLAGS(r9)
 	andi.	r0,r4,_TIF_NEED_RESCHED
 	bne	1b
 	b	restore
 
 user_work:
-#endif
+#endif /* CONFIG_PREEMPT */
+
 	/* Enable interrupts */
 #ifdef CONFIG_PPC_BOOK3E
 	wrteei	1
-- 
1.6.1.2.14.gf26b5

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Valentine]

Benjamin Herrenschmidt wrote:
>> So I _think_ that the irqs on/off accounting for lockdep isn't quite
>> right. What do you think of this slightly modified version ? I've only
>> done a quick boot test on a G5 with lockdep enabled and a played a bit,
>> nothing shows up so far but it's definitely not conclusive.
>>
>> The main difference is that I call trace_hardirqs_off to "advertise"
>> the fact that we are soft-disabling (it could be a dup, but at this
>> stage this is no big deal, but it's not always, like in syscall return
>> the kernel thinks we have interrupts enabled and could thus get out
>> of sync without that).
>>
>> I also mark the PACA hard disable to reflect the MSR:EE state before
>> calling into preempt_schedule_irq().
> 
> Allright, second thought :-)
> 
> It's probably simpler to just keep hardirqs off. Code is smaller and
> simpler and the scheduler will re-enable them soon enough anyways.
> 
> This version of the patch also spaces the code a bit and adds comments
> which makes them (the code and the patch) more readable.
> 

This one seems to work fine on pasemi and another maple-compatible board.

> Cheers,
> Ben.
>  
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> 
> [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule
> 
> Based on an original patch by Valentine Barshak <vbarshak@ru.mvista.com>
> 
> Use preempt_schedule_irq to prevent infinite irq-entry and
> eventual stack overflow problems with fast-paced IRQ sources.
> 
> This kind of problems has been observed on the PASemi Electra IDE
> controller. We have to make sure we are soft-disabled before calling
> preempt_schedule_irq and hard disable interrupts after that
> to avoid unrecoverable exceptions.
> 
> This patch also moves the "clrrdi r9,r1,THREAD_SHIFT" out of
> the #ifdef CONFIG_PPC_BOOK3E scope, since r9 is clobbered
> and has to be restored in both cases.
> ---
>  arch/powerpc/kernel/entry_64.S |   41 ++++++++++++++++++++-------------------
>  1 files changed, 21 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index f9fd54b..9763267 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -658,42 +658,43 @@ do_work:
>  	cmpdi	r0,0
>  	crandc	eq,cr1*4+eq,eq
>  	bne	restore
> -	/* here we are preempting the current task */
> -1:
> -#ifdef CONFIG_TRACE_IRQFLAGS
> -	bl	.trace_hardirqs_on
> -	/* Note: we just clobbered r10 which used to contain the previous
> -	 * MSR before the hard-disabling done by the caller of do_work.
> -	 * We don't have that value anymore, but it doesn't matter as
> -	 * we will hard-enable unconditionally, we can just reload the
> -	 * current MSR into r10
> +
> +	/* Here we are preempting the current task.
> +	 *
> +	 * Ensure interrupts are soft-disabled. We also properly mark
> +	 * the PACA to reflect the fact that they are hard-disabled
> +	 * and trace the change
>  	 */
> -	mfmsr	r10
> -#endif /* CONFIG_TRACE_IRQFLAGS */
> -	li	r0,1
> +	li	r0,0
>  	stb	r0,PACASOFTIRQEN(r13)
>  	stb	r0,PACAHARDIRQEN(r13)

I'm just not sure that we need to clear HARDIRQEN here, since we don't 
really hard-disable the the interrupts.

Thanks,
Val.

> +	TRACE_DISABLE_INTS
> +
> +	/* Call the scheduler with soft IRQs off */
> +1:	bl	.preempt_schedule_irq
> +
> +	/* Hard-disable interrupts again (and update PACA) */
>  #ifdef CONFIG_PPC_BOOK3E
> -	wrteei	1
> -	bl	.preempt_schedule
>  	wrteei	0
>  #else
> -	ori	r10,r10,MSR_EE
> -	mtmsrd	r10,1		/* reenable interrupts */
> -	bl	.preempt_schedule
>  	mfmsr	r10
> -	clrrdi	r9,r1,THREAD_SHIFT
> -	rldicl	r10,r10,48,1	/* disable interrupts again */
> +	rldicl	r10,r10,48,1
>  	rotldi	r10,r10,16
>  	mtmsrd	r10,1
>  #endif /* CONFIG_PPC_BOOK3E */
> +	li	r0,0
> +	stb	r0,PACAHARDIRQEN(r13)
> +
> +	/* Re-test flags and eventually loop */
> +	clrrdi	r9,r1,THREAD_SHIFT
>  	ld	r4,TI_FLAGS(r9)
>  	andi.	r0,r4,_TIF_NEED_RESCHED
>  	bne	1b
>  	b	restore
>  
>  user_work:
> -#endif
> +#endif /* CONFIG_PREEMPT */
> +
>  	/* Enable interrupts */
>  #ifdef CONFIG_PPC_BOOK3E
>  	wrteei	1

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Benjamin Herrenschmidt]

On Wed, 2009-10-28 at 22:19 +0300, Valentine wrote:

> I'm just not sure that we need to clear HARDIRQEN here, since we don't 
> really hard-disable the the interrupts.

We do, or rather, we come in with the interrupts hard disabled, no ?

Ben.

> Thanks,
> Val.
> 
> > +	TRACE_DISABLE_INTS
> > +
> > +	/* Call the scheduler with soft IRQs off */
> > +1:	bl	.preempt_schedule_irq
> > +
> > +	/* Hard-disable interrupts again (and update PACA) */
> >  #ifdef CONFIG_PPC_BOOK3E
> > -	wrteei	1
> > -	bl	.preempt_schedule
> >  	wrteei	0
> >  #else
> > -	ori	r10,r10,MSR_EE
> > -	mtmsrd	r10,1		/* reenable interrupts */
> > -	bl	.preempt_schedule
> >  	mfmsr	r10
> > -	clrrdi	r9,r1,THREAD_SHIFT
> > -	rldicl	r10,r10,48,1	/* disable interrupts again */
> > +	rldicl	r10,r10,48,1
> >  	rotldi	r10,r10,16
> >  	mtmsrd	r10,1
> >  #endif /* CONFIG_PPC_BOOK3E */
> > +	li	r0,0
> > +	stb	r0,PACAHARDIRQEN(r13)
> > +
> > +	/* Re-test flags and eventually loop */
> > +	clrrdi	r9,r1,THREAD_SHIFT
> >  	ld	r4,TI_FLAGS(r9)
> >  	andi.	r0,r4,_TIF_NEED_RESCHED
> >  	bne	1b
> >  	b	restore
> >  
> >  user_work:
> > -#endif
> > +#endif /* CONFIG_PREEMPT */
> > +
> >  	/* Enable interrupts */
> >  #ifdef CONFIG_PPC_BOOK3E
> >  	wrteei	1

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Valentine]

Benjamin Herrenschmidt wrote:
> On Wed, 2009-10-28 at 22:19 +0300, Valentine wrote:
> 
>> I'm just not sure that we need to clear HARDIRQEN here, since we don't 
>> really hard-disable the the interrupts.
> 
> We do, or rather, we come in with the interrupts hard disabled, no ?

Yes, looks like the interrupts are disabled at this point (before 
preempt_schedule_irq) most of the times, but we don't hard-disable them 
here. We just soft-disable them to make preempt_schedule_irq happy. Even 
if an interrupt fires, it will be hard-disabled and the hardirq flag 
will be cleared by the exception handler right away. I just think that 
there's no need to clear hardirq flag if we don't clear MSR_EE.

Thanks,
Val.
> 
> Ben.
> 
>> Thanks,
>> Val.
>>
>>> +	TRACE_DISABLE_INTS
>>> +
>>> +	/* Call the scheduler with soft IRQs off */
>>> +1:	bl	.preempt_schedule_irq
>>> +
>>> +	/* Hard-disable interrupts again (and update PACA) */
>>>  #ifdef CONFIG_PPC_BOOK3E
>>> -	wrteei	1
>>> -	bl	.preempt_schedule
>>>  	wrteei	0
>>>  #else
>>> -	ori	r10,r10,MSR_EE
>>> -	mtmsrd	r10,1		/* reenable interrupts */
>>> -	bl	.preempt_schedule
>>>  	mfmsr	r10
>>> -	clrrdi	r9,r1,THREAD_SHIFT
>>> -	rldicl	r10,r10,48,1	/* disable interrupts again */
>>> +	rldicl	r10,r10,48,1
>>>  	rotldi	r10,r10,16
>>>  	mtmsrd	r10,1
>>>  #endif /* CONFIG_PPC_BOOK3E */
>>> +	li	r0,0
>>> +	stb	r0,PACAHARDIRQEN(r13)
>>> +
>>> +	/* Re-test flags and eventually loop */
>>> +	clrrdi	r9,r1,THREAD_SHIFT
>>>  	ld	r4,TI_FLAGS(r9)
>>>  	andi.	r0,r4,_TIF_NEED_RESCHED
>>>  	bne	1b
>>>  	b	restore
>>>  
>>>  user_work:
>>> -#endif
>>> +#endif /* CONFIG_PREEMPT */
>>> +
>>>  	/* Enable interrupts */
>>>  #ifdef CONFIG_PPC_BOOK3E
>>>  	wrteei	1
> 
> 

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Benjamin Herrenschmidt]

On Thu, 2009-10-29 at 00:28 +0300, Valentine wrote:
> Benjamin Herrenschmidt wrote:
> > On Wed, 2009-10-28 at 22:19 +0300, Valentine wrote:
> > 
> >> I'm just not sure that we need to clear HARDIRQEN here, since we don't 
> >> really hard-disable the the interrupts.
> > 
> > We do, or rather, we come in with the interrupts hard disabled, no ?
> 
> Yes, looks like the interrupts are disabled at this point (before 
> preempt_schedule_irq) most of the times, but we don't hard-disable them 
> here. We just soft-disable them to make preempt_schedule_irq happy. Even 
> if an interrupt fires, it will be hard-disabled and the hardirq flag 
> will be cleared by the exception handler right away. I just think that 
> there's no need to clear hardirq flag if we don't clear MSR_EE.

My point is that MSR_EE _is_ already clear... isn't it ? So either we
set it back, or we clear HARDIRQEN to reflect it. It will be re-enable
as soon as preempt_schedule_irq() calls local_irq_enable() which is soon
enough anyways.

Also that avoids perf interrupt sneaking in since those act as NMIs in
that regard and -will- get in even when soft disabled.

Cheers,
Ben.

> Thanks,
> Val.
> > 
> > Ben.
> > 
> >> Thanks,
> >> Val.
> >>
> >>> +	TRACE_DISABLE_INTS
> >>> +
> >>> +	/* Call the scheduler with soft IRQs off */
> >>> +1:	bl	.preempt_schedule_irq
> >>> +
> >>> +	/* Hard-disable interrupts again (and update PACA) */
> >>>  #ifdef CONFIG_PPC_BOOK3E
> >>> -	wrteei	1
> >>> -	bl	.preempt_schedule
> >>>  	wrteei	0
> >>>  #else
> >>> -	ori	r10,r10,MSR_EE
> >>> -	mtmsrd	r10,1		/* reenable interrupts */
> >>> -	bl	.preempt_schedule
> >>>  	mfmsr	r10
> >>> -	clrrdi	r9,r1,THREAD_SHIFT
> >>> -	rldicl	r10,r10,48,1	/* disable interrupts again */
> >>> +	rldicl	r10,r10,48,1
> >>>  	rotldi	r10,r10,16
> >>>  	mtmsrd	r10,1
> >>>  #endif /* CONFIG_PPC_BOOK3E */
> >>> +	li	r0,0
> >>> +	stb	r0,PACAHARDIRQEN(r13)
> >>> +
> >>> +	/* Re-test flags and eventually loop */
> >>> +	clrrdi	r9,r1,THREAD_SHIFT
> >>>  	ld	r4,TI_FLAGS(r9)
> >>>  	andi.	r0,r4,_TIF_NEED_RESCHED
> >>>  	bne	1b
> >>>  	b	restore
> >>>  
> >>>  user_work:
> >>> -#endif
> >>> +#endif /* CONFIG_PREEMPT */
> >>> +
> >>>  	/* Enable interrupts */
> >>>  #ifdef CONFIG_PPC_BOOK3E
> >>>  	wrteei	1
> > 
> > 

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Valentine]

Benjamin Herrenschmidt wrote:
> On Thu, 2009-10-29 at 00:28 +0300, Valentine wrote:
>> Benjamin Herrenschmidt wrote:
>>> On Wed, 2009-10-28 at 22:19 +0300, Valentine wrote:
>>>
>>>> I'm just not sure that we need to clear HARDIRQEN here, since we don't 
>>>> really hard-disable the the interrupts.
>>> We do, or rather, we come in with the interrupts hard disabled, no ?
>> Yes, looks like the interrupts are disabled at this point (before 
>> preempt_schedule_irq) most of the times, but we don't hard-disable them 
>> here. We just soft-disable them to make preempt_schedule_irq happy. Even 
>> if an interrupt fires, it will be hard-disabled and the hardirq flag 
>> will be cleared by the exception handler right away. I just think that 
>> there's no need to clear hardirq flag if we don't clear MSR_EE.
> 
> My point is that MSR_EE _is_ already clear... isn't it ? 

Yes, the MSR_EE is cleared before we jump to do_work. I'm OK with 
clearing the hardirqenable flag. I just assumed that the hardirq flag 
was supposed to reflect the MSR_EE state, so it looked a bit odd 
clearing the MSR_EE at one place and then reflecting the change at another.

Anyway, the patch works fine.

Thanks,
Val.

So either we
> set it back, or we clear HARDIRQEN to reflect it. It will be re-enable
> as soon as preempt_schedule_irq() calls local_irq_enable() which is soon
> enough anyways.
> 
> Also that avoids perf interrupt sneaking in since those act as NMIs in
> that regard and -will- get in even when soft disabled.
> 
> Cheers,
> Ben.
> 
>> Thanks,
>> Val.
>>> Ben.
>>>
>>>> Thanks,
>>>> Val.
>>>>
>>>>> +	TRACE_DISABLE_INTS
>>>>> +
>>>>> +	/* Call the scheduler with soft IRQs off */
>>>>> +1:	bl	.preempt_schedule_irq
>>>>> +
>>>>> +	/* Hard-disable interrupts again (and update PACA) */
>>>>>  #ifdef CONFIG_PPC_BOOK3E
>>>>> -	wrteei	1
>>>>> -	bl	.preempt_schedule
>>>>>  	wrteei	0
>>>>>  #else
>>>>> -	ori	r10,r10,MSR_EE
>>>>> -	mtmsrd	r10,1		/* reenable interrupts */
>>>>> -	bl	.preempt_schedule
>>>>>  	mfmsr	r10
>>>>> -	clrrdi	r9,r1,THREAD_SHIFT
>>>>> -	rldicl	r10,r10,48,1	/* disable interrupts again */
>>>>> +	rldicl	r10,r10,48,1
>>>>>  	rotldi	r10,r10,16
>>>>>  	mtmsrd	r10,1
>>>>>  #endif /* CONFIG_PPC_BOOK3E */
>>>>> +	li	r0,0
>>>>> +	stb	r0,PACAHARDIRQEN(r13)
>>>>> +
>>>>> +	/* Re-test flags and eventually loop */
>>>>> +	clrrdi	r9,r1,THREAD_SHIFT
>>>>>  	ld	r4,TI_FLAGS(r9)
>>>>>  	andi.	r0,r4,_TIF_NEED_RESCHED
>>>>>  	bne	1b
>>>>>  	b	restore
>>>>>  
>>>>>  user_work:
>>>>> -#endif
>>>>> +#endif /* CONFIG_PREEMPT */
>>>>> +
>>>>>  	/* Enable interrupts */
>>>>>  #ifdef CONFIG_PPC_BOOK3E
>>>>>  	wrteei	1
>>>
> 
> 

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Benjamin Herrenschmidt]

> Yes, the MSR_EE is cleared before we jump to do_work. I'm OK with 
> clearing the hardirqenable flag. I just assumed that the hardirq flag 
> was supposed to reflect the MSR_EE state, so it looked a bit odd 
> clearing the MSR_EE at one place and then reflecting the change at another.

Yeah well, it is supposed to reflect EE in the "general case", it's just
that in the exception entry/exit, we take shortcuts when turning EE off
for short amount of times without reflecting it in the PACA. This is
why, in this case, since we are going back to C code, I want to have it
"fixed up" to reflect reality.

Cheers,
Ben.

> Anyway, the patch works fine.
> 
> Thanks,
> Val.
> 
> So either we
> > set it back, or we clear HARDIRQEN to reflect it. It will be re-enable
> > as soon as preempt_schedule_irq() calls local_irq_enable() which is soon
> > enough anyways.
> > 
> > Also that avoids perf interrupt sneaking in since those act as NMIs in
> > that regard and -will- get in even when soft disabled.
> > 
> > Cheers,
> > Ben.
> > 
> >> Thanks,
> >> Val.
> >>> Ben.
> >>>
> >>>> Thanks,
> >>>> Val.
> >>>>
> >>>>> +	TRACE_DISABLE_INTS
> >>>>> +
> >>>>> +	/* Call the scheduler with soft IRQs off */
> >>>>> +1:	bl	.preempt_schedule_irq
> >>>>> +
> >>>>> +	/* Hard-disable interrupts again (and update PACA) */
> >>>>>  #ifdef CONFIG_PPC_BOOK3E
> >>>>> -	wrteei	1
> >>>>> -	bl	.preempt_schedule
> >>>>>  	wrteei	0
> >>>>>  #else
> >>>>> -	ori	r10,r10,MSR_EE
> >>>>> -	mtmsrd	r10,1		/* reenable interrupts */
> >>>>> -	bl	.preempt_schedule
> >>>>>  	mfmsr	r10
> >>>>> -	clrrdi	r9,r1,THREAD_SHIFT
> >>>>> -	rldicl	r10,r10,48,1	/* disable interrupts again */
> >>>>> +	rldicl	r10,r10,48,1
> >>>>>  	rotldi	r10,r10,16
> >>>>>  	mtmsrd	r10,1
> >>>>>  #endif /* CONFIG_PPC_BOOK3E */
> >>>>> +	li	r0,0
> >>>>> +	stb	r0,PACAHARDIRQEN(r13)
> >>>>> +
> >>>>> +	/* Re-test flags and eventually loop */
> >>>>> +	clrrdi	r9,r1,THREAD_SHIFT
> >>>>>  	ld	r4,TI_FLAGS(r9)
> >>>>>  	andi.	r0,r4,_TIF_NEED_RESCHED
> >>>>>  	bne	1b
> >>>>>  	b	restore
> >>>>>  
> >>>>>  user_work:
> >>>>> -#endif
> >>>>> +#endif /* CONFIG_PREEMPT */
> >>>>> +
> >>>>>  	/* Enable interrupts */
> >>>>>  #ifdef CONFIG_PPC_BOOK3E
> >>>>>  	wrteei	1
> >>>
> > 
> > 

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Valentine]

Benjamin Herrenschmidt wrote:
>> Yes, the MSR_EE is cleared before we jump to do_work. I'm OK with 
>> clearing the hardirqenable flag. I just assumed that the hardirq flag 
>> was supposed to reflect the MSR_EE state, so it looked a bit odd 
>> clearing the MSR_EE at one place and then reflecting the change at another.
> 
> Yeah well, it is supposed to reflect EE in the "general case", it's just
> that in the exception entry/exit, we take shortcuts when turning EE off
> for short amount of times without reflecting it in the PACA. This is
> why, in this case, since we are going back to C code, I want to have it
> "fixed up" to reflect reality.
> 

Ben, this one works fine. Are you going to pick it?

Thanks,
Val.

Re: [PATCH v3] powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule

[Benjamin Herrenschmidt]

On Sat, 2009-11-07 at 01:38 +0300, Valentine wrote:
> Benjamin Herrenschmidt wrote:
> >> Yes, the MSR_EE is cleared before we jump to do_work. I'm OK with 
> >> clearing the hardirqenable flag. I just assumed that the hardirq flag 
> >> was supposed to reflect the MSR_EE state, so it looked a bit odd 
> >> clearing the MSR_EE at one place and then reflecting the change at another.
> > 
> > Yeah well, it is supposed to reflect EE in the "general case", it's just
> > that in the exception entry/exit, we take shortcuts when turning EE off
> > for short amount of times without reflecting it in the PACA. This is
> > why, in this case, since we are going back to C code, I want to have it
> > "fixed up" to reflect reality.
> > 
> 
> Ben, this one works fine. Are you going to pick it?

Already upstream:

Gitweb:
http://git.kernel.org/linus/4f917ba3d5ee9c98d60fa357e799942df8412de3
Commit:     4f917ba3d5ee9c98d60fa357e799942df8412de3
Parent:     01deab98e3ad8ff27243a8d5f8dd746c7110ae4f
Author:     Benjamin Herrenschmidt <benh@kernel.crashing.org>
AuthorDate: Mon Oct 26 19:41:17 2009 +0000
Committer:  Benjamin Herrenschmidt <benh@kernel.crashing.org>
CommitDate: Tue Oct 27 16:42:43 2009 +1100

    powerpc/ppc64: Use preempt_schedule_irq instead of preempt_schedule
    
    Based on an original patch by Valentine Barshak <vbarshak@ru.mvista.com>
    
    Use preempt_schedule_irq to prevent infinite irq-entry and
    eventual stack overflow problems with fast-paced IRQ sources.

    .../...

Now, it might be a good idea to do a -stable variant of it for 2.6.31
and back, but that will have to be a separate patch due to the new
Book3E churn in .32

Cheers,
Ben.