From: David Miller on

I'm rescinding these patches for now, for two reasons:

1) The NMI annotations necessary to get everything working really gets
out of control.

2) I think I found a cheap way to do this in sparc64 specific code.

Thanks!
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From: Peter Zijlstra on
On Mon, 2010-04-12 at 22:08 -0700, David Miller wrote:
> I'm rescinding these patches for now, for two reasons:
>
> 1) The NMI annotations necessary to get everything working really gets
> out of control.
>
> 2) I think I found a cheap way to do this in sparc64 specific code.

Ah, ok..

Care to enlighten the curious amongst us as to what exactly you're doing
in the sparc code?
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From: David Miller on
From: Peter Zijlstra <peterz(a)infradead.org>
Date: Tue, 13 Apr 2010 09:48:58 +0200

> Care to enlighten the curious amongst us as to what exactly you're
> doing in the sparc code?

From 0c25e9e6cbe7b233bb91d14d0e2c258bf8e6ec83 Mon Sep 17 00:00:00 2001
From: David S. Miller <davem(a)davemloft.net>
Date: Mon, 12 Apr 2010 22:21:52 -0700
Subject: [PATCH 2/2] sparc64: Adjust __raw_local_irq_save() to cooperate in NMIs.

If we are in an NMI then doing a plain raw_local_irq_disable() will
write PIL_NORMAL_MAX into %pil, which is lower than PIL_NMI, and thus
we'll re-enable NMIs and recurse.

Doing a simple:

%pil = %pil | PIL_NORMAL_MAX

does what we want, if we're already at PIL_NMI (15) we leave it at
that setting, else we set it to PIL_NORMAL_MAX (14).

This should get the function tracer working on sparc64.

Signed-off-by: David S. Miller <davem(a)davemloft.net>
---
arch/sparc/include/asm/irqflags_64.h | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/sparc/include/asm/irqflags_64.h b/arch/sparc/include/asm/irqflags_64.h
index 8b49bf9..a16e94c 100644
--- a/arch/sparc/include/asm/irqflags_64.h
+++ b/arch/sparc/include/asm/irqflags_64.h
@@ -76,9 +76,19 @@ static inline int raw_irqs_disabled(void)
*/
static inline unsigned long __raw_local_irq_save(void)
{
- unsigned long flags = __raw_local_save_flags();
+ unsigned long flags, tmp;

- raw_local_irq_disable();
+ /* Disable interrupts to PIL_NORMAL_MAX unless we already
+ * are using PIL_NMI, in which case PIL_NMI is retained.
+ */
+ __asm__ __volatile__(
+ "rdpr %%pil, %0\n\t"
+ "or %0, %2, %1\n\t"
+ "wrpr %1, 0x0, %%pil"
+ : "=r" (flags), "=r" (tmp)
+ : "i" (PIL_NORMAL_MAX)
+ : "memory"
+ );

return flags;
}
--
1.7.0.4

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From: Peter Zijlstra on
On Tue, 2010-04-13 at 00:56 -0700, David Miller wrote:

> If we are in an NMI then doing a plain raw_local_irq_disable() will
> write PIL_NORMAL_MAX into %pil, which is lower than PIL_NMI, and thus
> we'll re-enable NMIs and recurse.
>
> Doing a simple:
>
> %pil = %pil | PIL_NORMAL_MAX
>
> does what we want, if we're already at PIL_NMI (15) we leave it at
> that setting, else we set it to PIL_NORMAL_MAX (14).

Ah indeed, and without a conditional, very nice!

It does rely on the exact values of the PIL_levels, it might make sense
to note that in the comment, something like:

* Assumes: PIL_NMI | PIL_NORMAL_MAX == PIL_NMI.

Hmm, it also assumes %pil is never anything other than 0,
PIL_NORMAL_MAX, PIL_NMI, because if:

(%pil & 1) && (%pil != PIL_NMI)

then you'll end up disabling NMIs. Could something like that ever
happen?


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From: David Miller on
From: Peter Zijlstra <peterz(a)infradead.org>
Date: Tue, 13 Apr 2010 10:37:14 +0200

> Hmm, it also assumes %pil is never anything other than 0,
> PIL_NORMAL_MAX, PIL_NMI, because if:
>
> (%pil & 1) && (%pil != PIL_NMI)
>
> then you'll end up disabling NMIs. Could something like that ever
> happen?

The only values we ever program into the %pil are 0, PIL_NORMAL_MAX
and PIL_NMI

Since PIL_NMI is the largest %pil value and all bits are set in it
(0xf), it doesn't matter what PIL_NORMAL_MAX actually is.

Yes this all deserves a comment, I'll add one, thanks for pointing
that out.
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