ARM: Add safe diagnostic to indicate when __cpu_architecture isn't set up

PATCH New Dave Martin 3 participants 6 messages Aug 16, 2011 – Aug 17, 2011 Arm (32-bit)

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Dave Martin

author

2011-08-16 14:19 UTC #0 lore raw

PATCH 1/1 ARM: Add safe diagnostic to indicate when __cpu_architecture isn't set up

Although assing BUG() when __cpu_architecture is unexpectedly CPU_ARCH_UNKNOWN seems like a good idea, in practice the kernel may not be able to boot far enough even to write to the console in such cases, even with earlyprintk enabled.

This patch adds a more useful diagnostic, and works out the cpu architecture from scratch in such cases, instead of just returning CPU_ARCH_UNKNOWN to the caller.

This patch is useful for debugging, but I'm not convinced it should be merged.

Signed-off-by Dave Martin <[email protected]>

---
 arch/arm/include/asm/system.h |    9 +++++++--
 arch/arm/kernel/setup.c       |    2 +-
 2 files changed, 8 insertions(+), 3 deletions(-)

arch/arm/include/asm/system.h +7 -2

index b0445f7..d679d2f 100644
@@ -110,8 +110,13 @@ extern int __cpu_architecture;
 
 static inline int __pure cpu_architecture(void)
 {
-	BUG_ON(__cpu_architecture == CPU_ARCH_UNKNOWN);
-	return __cpu_architecture;
+	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN)) {
+		extern int __pure __get_cpu_architecture(void);
+
+		WARN_ONCE(1, "__cpu_architecture not set yet!\n");
+		return __get_cpu_architecture();
+	} else
+		return __cpu_architecture;
 }
 
 extern void cpu_init(void);

arch/arm/kernel/setup.c +1 -1

index 1e0c1b3..188aae5 100644
@@ -212,7 +212,7 @@ static const char *proc_arch[] = {
 	"?(17)",
 };
 
-static int __init __get_cpu_architecture(void)
+int __get_cpu_architecture(void)
 {
 	int cpu_arch;

Signature · 1 line

1.7.4.1

Tixy

2011-08-16 14:45 UTC #1 lore raw

PATCH 1/1 ARM: Add safe diagnostic to indicate when __cpu_architecture isn't set up

On Tue, 2011-08-16 at 15:19 +0100, Dave Martin wrote:
[...]

Quoted 2 lines

This patch is useful for debugging, but I'm not convinced it should be merged.

[...]

arch/arm/include/asm/system.h extern int __cpu_architecture; · line 120

Quoted 12 lines

static inline int __pure cpu_architecture(void)
{

arch/arm/include/asm/system.h +7 -2

-	BUG_ON(__cpu_architecture == CPU_ARCH_UNKNOWN);
-	return __cpu_architecture;
+	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN)) {
+		extern int __pure __get_cpu_architecture(void);
+
+		WARN_ONCE(1, "__cpu_architecture not set yet!\n");
+		return __get_cpu_architecture();
+	} else
+		return __cpu_architecture;
 }

Seems to me that if we go down this route, cpu_architecture() may as well remain a non-inline function which just calculates the arch if it's not already set...

	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN))
		__cpu_architecture = __get_cpu_architecture();
	return __cpu_architecture;

There seems to be too many ways to skin this cat :-)

Signature · 1 line

Tixy

Nicolas Pitre

2011-08-16 14:59 UTC #2 lore raw

PATCH 1/1 ARM: Add safe diagnostic to indicate when __cpu_architecture isn't set up

Quoted 5 lines · Tixy

On Tue, 2011-08-16 at 15:19 +0100, Dave Martin wrote:
[...]
Quoted 2 lines
This patch is useful for debugging, but I'm not convinced it should be merged.
[...]

Quoted 16 lines

arch/arm/include/asm/system.h extern int __cpu_architecture; · line 120
Quoted 12 lines
static inline int __pure cpu_architecture(void)
{
arch/arm/include/asm/system.h +7 -2
-	BUG_ON(__cpu_architecture == CPU_ARCH_UNKNOWN);
-	return __cpu_architecture;
+	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN)) {
+		extern int __pure __get_cpu_architecture(void);
+
+		WARN_ONCE(1, "__cpu_architecture not set yet!\n");
+		return __get_cpu_architecture();
+	} else
+		return __cpu_architecture;
 }
Seems to me that if we go down this route, cpu_architecture() may as well remain a non-inline function which just calculates the arch if it's not already set...

My thought as well.

Quoted 5 lines

	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN))
		__cpu_architecture = __get_cpu_architecture();
	return __cpu_architecture;

There seems to be too many ways to skin this cat :-)

Agreed.

Nicolas

Dave Martin

author

2011-08-16 16:15 UTC #3 lore raw

PATCH 1/1 ARM: Add safe diagnostic to indicate when __cpu_architecture isn't set up

Quoted 26 lines · Nicolas Pitre

Quoted 5 lines · Tixy
On Tue, 2011-08-16 at 15:19 +0100, Dave Martin wrote:
[...]
Quoted 2 lines
This patch is useful for debugging, but I'm not convinced it should be merged.
[...]
Quoted 16 lines
arch/arm/include/asm/system.h extern int __cpu_architecture; · line 120
Quoted 12 lines
static inline int __pure cpu_architecture(void)
{
arch/arm/include/asm/system.h +7 -2
-	BUG_ON(__cpu_architecture == CPU_ARCH_UNKNOWN);
-	return __cpu_architecture;
+	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN)) {
+		extern int __pure __get_cpu_architecture(void);
+
+		WARN_ONCE(1, "__cpu_architecture not set yet!\n");
+		return __get_cpu_architecture();
+	} else
+		return __cpu_architecture;
 }
Seems to me that if we go down this route, cpu_architecture() may as well remain a non-inline function which just calculates the arch if it's not already set...
My thought as well.

Quoted 7 lines

Quoted 5 lines
	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN))
		__cpu_architecture = __get_cpu_architecture();
	return __cpu_architecture;
There seems to be too many ways to skin this cat :-)
Agreed.

Well, I guess the flipside is, do we need this check at all?

Because __cpu_architecture is set really early, and because if it's referenced too early, the kernel will either not boot or we'll hit BUG(), it's hard to imaging such a failure going unnoticed.

So this check could simply be viewed as overkill, though it does feel safer to check.

Any thoughts?

---Dave

Nicolas Pitre

2011-08-16 16:22 UTC #4 lore raw

PATCH 1/1 ARM: Add safe diagnostic to indicate when __cpu_architecture isn't set up

Quoted 37 lines · Dave Martin

Quoted 26 lines · Nicolas Pitre
Quoted 5 lines · Tixy
On Tue, 2011-08-16 at 15:19 +0100, Dave Martin wrote:
[...]
Quoted 2 lines
This patch is useful for debugging, but I'm not convinced it should be merged.
[...]
Quoted 16 lines
arch/arm/include/asm/system.h extern int __cpu_architecture; · line 120
Quoted 12 lines
static inline int __pure cpu_architecture(void)
{
arch/arm/include/asm/system.h +7 -2
-	BUG_ON(__cpu_architecture == CPU_ARCH_UNKNOWN);
-	return __cpu_architecture;
+	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN)) {
+		extern int __pure __get_cpu_architecture(void);
+
+		WARN_ONCE(1, "__cpu_architecture not set yet!\n");
+		return __get_cpu_architecture();
+	} else
+		return __cpu_architecture;
 }
Seems to me that if we go down this route, cpu_architecture() may as well remain a non-inline function which just calculates the arch if it's not already set...
My thought as well.
Quoted 7 lines
Quoted 5 lines
	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN))
		__cpu_architecture = __get_cpu_architecture();
	return __cpu_architecture;
There seems to be too many ways to skin this cat :-)
Agreed.
Well, I guess the flipside is, do we need this check at all?

Quoted 8 lines

Because __cpu_architecture is set really early, and because if it's referenced too early, the kernel will either not boot or we'll hit BUG(), it's hard to imaging such a failure going unnoticed.
So this check could simply be viewed as overkill, though it does feel safer to check.
Any thoughts?

I personally think this is overkill.

Nicolas

Dave Martin

author

2011-08-17 10:53 UTC #5 lore raw

PATCH 1/1 ARM: Add safe diagnostic to indicate when __cpu_architecture isn't set up

Quoted 43 lines · Nicolas Pitre

Quoted 41 lines · Dave Martin
Quoted 26 lines · Nicolas Pitre
Quoted 5 lines · Tixy
On Tue, 2011-08-16 at 15:19 +0100, Dave Martin wrote:
[...]
Quoted 2 lines
This patch is useful for debugging, but I'm not convinced it should be merged.
[...]
Quoted 16 lines
arch/arm/include/asm/system.h extern int __cpu_architecture; · line 120
Quoted 12 lines
static inline int __pure cpu_architecture(void)
{
arch/arm/include/asm/system.h +7 -2
-	BUG_ON(__cpu_architecture == CPU_ARCH_UNKNOWN);
-	return __cpu_architecture;
+	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN)) {
+		extern int __pure __get_cpu_architecture(void);
+
+		WARN_ONCE(1, "__cpu_architecture not set yet!\n");
+		return __get_cpu_architecture();
+	} else
+		return __cpu_architecture;
 }
Seems to me that if we go down this route, cpu_architecture() may as well remain a non-inline function which just calculates the arch if it's not already set...
My thought as well.
Quoted 7 lines
Quoted 5 lines
	if (unlikely(__cpu_architecture == CPU_ARCH_UNKNOWN))
		__cpu_architecture = __get_cpu_architecture();
	return __cpu_architecture;
There seems to be too many ways to skin this cat :-)
Agreed.
Well, I guess the flipside is, do we need this check at all?
Because __cpu_architecture is set really early, and because if it's referenced too early, the kernel will either not boot or we'll hit BUG(), it's hard to imaging such a failure going unnoticed.

Quoted 6 lines

Quoted 4 lines
So this check could simply be viewed as overkill, though it does feel safer to check.
Any thoughts?
I personally think this is overkill.

OK, well since the inlining of cpu_architecture() doesn't feel like it really brings us any benefits I may move it back out of line, into setup.c, but keeping its new definition, including BUG(). The only reason for moving that function to be inline was because it had become trivial, but putting BUG() back undermines that.

I will also remove the declaration of __cpu_architecture from <asm/system.h>, since for now this should not be used directly at all except by the undef handler, and we don't want to encourage its use.

Any concerns on all of that?

In the meantime, I will re-roll those patches... hopefully for the final time.

Cheers
---Dave