[PATCH] lockdep: annotate i386 apm

[PATCH] lockdep: annotate i386 apm

[Peter Zijlstra]

Lockdep doesn't like to enable interrupts when they are enabled already.

BUG: warning at kernel/lockdep.c:1814/trace_hardirqs_on() (Not tainted)
 [<c04051ed>] show_trace_log_lvl+0x58/0x16a
 [<c04057fa>] show_trace+0xd/0x10
 [<c0405913>] dump_stack+0x19/0x1b
 [<c043abfb>] trace_hardirqs_on+0xa2/0x11e
 [<c041463c>] apm_bios_call_simple+0xcd/0xfd
 [<c0415242>] apm+0x92/0x5b1
 [<c0402005>] kernel_thread_helper+0x5/0xb
DWARF2 unwinder stuck at kernel_thread_helper+0x5/0xb
Leftover inexact backtrace:
 [<c04057fa>] show_trace+0xd/0x10
 [<c0405913>] dump_stack+0x19/0x1b
 [<c043abfb>] trace_hardirqs_on+0xa2/0x11e
 [<c041463c>] apm_bios_call_simple+0xcd/0xfd
 [<c0415242>] apm+0x92/0x5b1
 [<c0402005>] kernel_thread_helper+0x5/0xb

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 arch/i386/kernel/apm.c |   25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

Index: linux-2.6.18.noarch/arch/i386/kernel/apm.c
===================================================================
--- linux-2.6.18.noarch.orig/arch/i386/kernel/apm.c
+++ linux-2.6.18.noarch/arch/i386/kernel/apm.c
@@ -539,11 +539,22 @@ static inline void apm_restore_cpus(cpum
  * Also, we KNOW that for the non error case of apm_bios_call, there
  * is no useful data returned in the low order 8 bits of eax.
  */
-#define APM_DO_CLI	\
-	if (apm_info.allow_ints) \
-		local_irq_enable(); \
-	else \
-		local_irq_disable();
+#define APM_DO_CLI \
+	do { \
+		if (apm_info.allow_ints) { \
+			if (irqs_disabled_flags(flags)) \
+				local_irq_enable(); \
+		} else \
+			local_irq_disable(); \
+	} while (0)
+
+#define APM_DO_STI \
+	do { \
+		if (irqs_disabled_flags(flags)) \
+			local_irq_disable(); \
+		else if (irqs_disabled()) \
+			local_irq_enable(); \
+	} while (0)
 
 #ifdef APM_ZERO_SEGS
 #	define APM_DECL_SEGS \
@@ -600,7 +611,7 @@ static u8 apm_bios_call(u32 func, u32 eb
 	APM_DO_SAVE_SEGS;
 	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
 	APM_DO_RESTORE_SEGS;
-	local_irq_restore(flags);
+	APM_DO_STI;
 	gdt[0x40 / 8] = save_desc_40;
 	put_cpu();
 	apm_restore_cpus(cpus);
@@ -644,7 +655,7 @@ static u8 apm_bios_call_simple(u32 func,
 	APM_DO_SAVE_SEGS;
 	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
 	APM_DO_RESTORE_SEGS;
-	local_irq_restore(flags);
+	APM_DO_STI;
 	gdt[0x40 / 8] = save_desc_40;
 	put_cpu();
 	apm_restore_cpus(cpus);

Re: [PATCH] lockdep: annotate i386 apm

[Andrew Morton]

On Wed, 11 Oct 2006 15:40:22 +0200
Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> 
> Lockdep doesn't like to enable interrupts when they are enabled already.
> 
> ...
>
> --- linux-2.6.18.noarch.orig/arch/i386/kernel/apm.c
> +++ linux-2.6.18.noarch/arch/i386/kernel/apm.c
> @@ -539,11 +539,22 @@ static inline void apm_restore_cpus(cpum
>   * Also, we KNOW that for the non error case of apm_bios_call, there
>   * is no useful data returned in the low order 8 bits of eax.
>   */
> -#define APM_DO_CLI	\
> -	if (apm_info.allow_ints) \
> -		local_irq_enable(); \
> -	else \
> -		local_irq_disable();
> +#define APM_DO_CLI \
> +	do { \
> +		if (apm_info.allow_ints) { \
> +			if (irqs_disabled_flags(flags)) \
> +				local_irq_enable(); \
> +		} else \
> +			local_irq_disable(); \
> +	} while (0)
> +
> +#define APM_DO_STI \
> +	do { \
> +		if (irqs_disabled_flags(flags)) \
> +			local_irq_disable(); \
> +		else if (irqs_disabled()) \
> +			local_irq_enable(); \
> +	} while (0)
>  
>  #ifdef APM_ZERO_SEGS
>  #	define APM_DECL_SEGS \
> @@ -600,7 +611,7 @@ static u8 apm_bios_call(u32 func, u32 eb
>  	APM_DO_SAVE_SEGS;
>  	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
>  	APM_DO_RESTORE_SEGS;
> -	local_irq_restore(flags);
> +	APM_DO_STI;
>  	gdt[0x40 / 8] = save_desc_40;
>  	put_cpu();
>  	apm_restore_cpus(cpus);
> @@ -644,7 +655,7 @@ static u8 apm_bios_call_simple(u32 func,
>  	APM_DO_SAVE_SEGS;
>  	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
>  	APM_DO_RESTORE_SEGS;
> -	local_irq_restore(flags);
> +	APM_DO_STI;
>  	gdt[0x40 / 8] = save_desc_40;
>  	put_cpu();
>  	apm_restore_cpus(cpus);

ick.

Does this work?

--- a/arch/i386/kernel/apm.c~lockdep-annotate-i386-apm
+++ a/arch/i386/kernel/apm.c
@@ -540,12 +540,6 @@ static inline void apm_restore_cpus(cpum
  * Also, we KNOW that for the non error case of apm_bios_call, there
  * is no useful data returned in the low order 8 bits of eax.
  */
-#define APM_DO_CLI	\
-	if (apm_info.allow_ints) \
-		local_irq_enable(); \
-	else \
-		local_irq_disable();
-
 #ifdef APM_ZERO_SEGS
 #	define APM_DECL_SEGS \
 		unsigned int saved_fs; unsigned int saved_gs;
@@ -596,8 +590,9 @@ static u8 apm_bios_call(u32 func, u32 eb
 	save_desc_40 = gdt[0x40 / 8];
 	gdt[0x40 / 8] = bad_bios_desc;
 
-	local_save_flags(flags);
-	APM_DO_CLI;
+	local_irq_save(flags);
+	if (apm_info.allow_ints)
+		local_irq_enable();
 	APM_DO_SAVE_SEGS;
 	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
 	APM_DO_RESTORE_SEGS;
@@ -640,8 +635,9 @@ static u8 apm_bios_call_simple(u32 func,
 	save_desc_40 = gdt[0x40 / 8];
 	gdt[0x40 / 8] = bad_bios_desc;
 
-	local_save_flags(flags);
-	APM_DO_CLI;
+	local_irq_save(flags);
+	if (apm_info.allow_ints)
+		local_irq_enable();
 	APM_DO_SAVE_SEGS;
 	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
 	APM_DO_RESTORE_SEGS;
_

Re: [PATCH] lockdep: annotate i386 apm

[Peter Zijlstra]

On Wed, 2006-10-11 at 14:18 -0700, Andrew Morton wrote:
> On Wed, 11 Oct 2006 15:40:22 +0200
> Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> 
> > 
> > Lockdep doesn't like to enable interrupts when they are enabled already.
> > 
> > ...
> >
> > --- linux-2.6.18.noarch.orig/arch/i386/kernel/apm.c
> > +++ linux-2.6.18.noarch/arch/i386/kernel/apm.c
> > @@ -539,11 +539,22 @@ static inline void apm_restore_cpus(cpum
> >   * Also, we KNOW that for the non error case of apm_bios_call, there
> >   * is no useful data returned in the low order 8 bits of eax.
> >   */
> > -#define APM_DO_CLI	\
> > -	if (apm_info.allow_ints) \
> > -		local_irq_enable(); \
> > -	else \
> > -		local_irq_disable();
> > +#define APM_DO_CLI \
> > +	do { \
> > +		if (apm_info.allow_ints) { \
> > +			if (irqs_disabled_flags(flags)) \
> > +				local_irq_enable(); \
> > +		} else \
> > +			local_irq_disable(); \
> > +	} while (0)
> > +
> > +#define APM_DO_STI \
> > +	do { \
> > +		if (irqs_disabled_flags(flags)) \
> > +			local_irq_disable(); \
> > +		else if (irqs_disabled()) \
> > +			local_irq_enable(); \
> > +	} while (0)
> >  
> >  #ifdef APM_ZERO_SEGS
> >  #	define APM_DECL_SEGS \
> > @@ -600,7 +611,7 @@ static u8 apm_bios_call(u32 func, u32 eb
> >  	APM_DO_SAVE_SEGS;
> >  	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
> >  	APM_DO_RESTORE_SEGS;
> > -	local_irq_restore(flags);
> > +	APM_DO_STI;
> >  	gdt[0x40 / 8] = save_desc_40;
> >  	put_cpu();
> >  	apm_restore_cpus(cpus);
> > @@ -644,7 +655,7 @@ static u8 apm_bios_call_simple(u32 func,
> >  	APM_DO_SAVE_SEGS;
> >  	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
> >  	APM_DO_RESTORE_SEGS;
> > -	local_irq_restore(flags);
> > +	APM_DO_STI;
> >  	gdt[0x40 / 8] = save_desc_40;
> >  	put_cpu();
> >  	apm_restore_cpus(cpus);
> 
> ick.
> 
> Does this work?
> 
> --- a/arch/i386/kernel/apm.c~lockdep-annotate-i386-apm
> +++ a/arch/i386/kernel/apm.c
> @@ -540,12 +540,6 @@ static inline void apm_restore_cpus(cpum
>   * Also, we KNOW that for the non error case of apm_bios_call, there
>   * is no useful data returned in the low order 8 bits of eax.
>   */
> -#define APM_DO_CLI	\
> -	if (apm_info.allow_ints) \
> -		local_irq_enable(); \
> -	else \
> -		local_irq_disable();
> -
>  #ifdef APM_ZERO_SEGS
>  #	define APM_DECL_SEGS \
>  		unsigned int saved_fs; unsigned int saved_gs;
> @@ -596,8 +590,9 @@ static u8 apm_bios_call(u32 func, u32 eb
>  	save_desc_40 = gdt[0x40 / 8];
>  	gdt[0x40 / 8] = bad_bios_desc;
>  
> -	local_save_flags(flags);
> -	APM_DO_CLI;
> +	local_irq_save(flags);
> +	if (apm_info.allow_ints)
> +		local_irq_enable();
>  	APM_DO_SAVE_SEGS;
>  	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
>  	APM_DO_RESTORE_SEGS;
> @@ -640,8 +635,9 @@ static u8 apm_bios_call_simple(u32 func,
>  	save_desc_40 = gdt[0x40 / 8];
>  	gdt[0x40 / 8] = bad_bios_desc;
>  
> -	local_save_flags(flags);
> -	APM_DO_CLI;
> +	local_irq_save(flags);
> +	if (apm_info.allow_ints)
> +		local_irq_enable();
>  	APM_DO_SAVE_SEGS;
>  	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
>  	APM_DO_RESTORE_SEGS;
> _

#define local_irq_restore(flags)                                \
        do {                                                    \
                if (raw_irqs_disabled_flags(flags)) {           \
                        raw_local_irq_restore(flags);           \
                        trace_hardirqs_off();                   \
                } else {                                        \
                        trace_hardirqs_on();                    \
                        raw_local_irq_restore(flags);           \
                }                                               \
        } while (0)

So, say interrupts were enabled when entering apm_bios_call*(); you now
save that in flags, disable interrupts, and enable them again.
Upon reaching local_irq_restore(), we'll hit the else branch with irq's
enabled and call trace_hardirqs_on(), which goes EEEK!

Re: [PATCH] lockdep: annotate i386 apm

[Andrew Morton]

On Thu, 12 Oct 2006 08:06:20 +0200
Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> #define local_irq_restore(flags)                                \
>         do {                                                    \
>                 if (raw_irqs_disabled_flags(flags)) {           \
>                         raw_local_irq_restore(flags);           \
>                         trace_hardirqs_off();                   \
>                 } else {                                        \
>                         trace_hardirqs_on();                    \
>                         raw_local_irq_restore(flags);           \
>                 }                                               \
>         } while (0)
> 
> So, say interrupts were enabled when entering apm_bios_call*(); you now
> save that in flags, disable interrupts, and enable them again.
> Upon reaching local_irq_restore(), we'll hit the else branch with irq's
> enabled and call trace_hardirqs_on(), which goes EEEK!

I'd assumed lockdep was less stupid than that ;) This?  Seems a bit
overdone..

--- a/arch/i386/kernel/apm.c~lockdep-annotate-i386-apm
+++ a/arch/i386/kernel/apm.c
@@ -540,12 +540,6 @@ static inline void apm_restore_cpus(cpum
  * Also, we KNOW that for the non error case of apm_bios_call, there
  * is no useful data returned in the low order 8 bits of eax.
  */
-#define APM_DO_CLI	\
-	if (apm_info.allow_ints) \
-		local_irq_enable(); \
-	else \
-		local_irq_disable();
-
 #ifdef APM_ZERO_SEGS
 #	define APM_DECL_SEGS \
 		unsigned int saved_fs; unsigned int saved_gs;
@@ -583,11 +577,12 @@ static u8 apm_bios_call(u32 func, u32 eb
 	u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, u32 *esi)
 {
 	APM_DECL_SEGS
-	unsigned long		flags;
 	cpumask_t		cpus;
 	int			cpu;
 	struct desc_struct	save_desc_40;
 	struct desc_struct	*gdt;
+	int			enable_irqs = 0;
+	int			disable_irqs = 0;
 
 	cpus = apm_save_cpus();
 	
@@ -596,12 +591,26 @@ static u8 apm_bios_call(u32 func, u32 eb
 	save_desc_40 = gdt[0x40 / 8];
 	gdt[0x40 / 8] = bad_bios_desc;
 
-	local_save_flags(flags);
-	APM_DO_CLI;
+	if (apm_info.allow_ints) {
+		if (irqs_disabled()) {
+			local_irq_enable();
+			disable_irqs = 1;
+		}
+	} else {
+		if (!irqs_disabled()) {
+			local_irq_disable();
+			enable_irqs = 1;
+		}
+	}
+
+
 	APM_DO_SAVE_SEGS;
 	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
 	APM_DO_RESTORE_SEGS;
-	local_irq_restore(flags);
+	if (disable_irqs)
+		local_irq_disable();
+	if (enable_irqs)
+		local_irq_enable();
 	gdt[0x40 / 8] = save_desc_40;
 	put_cpu();
 	apm_restore_cpus(cpus);
@@ -627,11 +636,12 @@ static u8 apm_bios_call_simple(u32 func,
 {
 	u8			error;
 	APM_DECL_SEGS
-	unsigned long		flags;
 	cpumask_t		cpus;
 	int			cpu;
 	struct desc_struct	save_desc_40;
 	struct desc_struct	*gdt;
+	int			enable_irqs = 0;
+	int			disable_irqs = 0;
 
 	cpus = apm_save_cpus();
 	
@@ -640,12 +650,25 @@ static u8 apm_bios_call_simple(u32 func,
 	save_desc_40 = gdt[0x40 / 8];
 	gdt[0x40 / 8] = bad_bios_desc;
 
-	local_save_flags(flags);
-	APM_DO_CLI;
+	if (apm_info.allow_ints) {
+		if (irqs_disabled()) {
+			local_irq_enable();
+			disable_irqs = 1;
+		}
+	} else {
+		if (!irqs_disabled()) {
+			local_irq_disable();
+			enable_irqs = 1;
+		}
+	}
+
 	APM_DO_SAVE_SEGS;
 	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
 	APM_DO_RESTORE_SEGS;
-	local_irq_restore(flags);
+	if (disable_irqs)
+		local_irq_disable();
+	if (enable_irqs)
+		local_irq_enable();
 	gdt[0x40 / 8] = save_desc_40;
 	put_cpu();
 	apm_restore_cpus(cpus);
_

Re: [PATCH] lockdep: annotate i386 apm

[Peter Zijlstra]

On Wed, 2006-10-11 at 23:39 -0700, Andrew Morton wrote:
> On Thu, 12 Oct 2006 08:06:20 +0200
> Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> 
> > #define local_irq_restore(flags)                                \
> >         do {                                                    \
> >                 if (raw_irqs_disabled_flags(flags)) {           \
> >                         raw_local_irq_restore(flags);           \
> >                         trace_hardirqs_off();                   \
> >                 } else {                                        \
> >                         trace_hardirqs_on();                    \
> >                         raw_local_irq_restore(flags);           \
> >                 }                                               \
> >         } while (0)
> > 
> > So, say interrupts were enabled when entering apm_bios_call*(); you now
> > save that in flags, disable interrupts, and enable them again.
> > Upon reaching local_irq_restore(), we'll hit the else branch with irq's
> > enabled and call trace_hardirqs_on(), which goes EEEK!
> 
> I'd assumed lockdep was less stupid than that ;) This?  Seems a bit
> overdone..

Seems simple enough, bit on the verbose side, _however_ it depends on
the BIOS call not changing the irq state. I don't know about BIOSs but I
thought the general consensus was to distrust them.

Was my original _that_ hard to read?

> --- a/arch/i386/kernel/apm.c~lockdep-annotate-i386-apm
> +++ a/arch/i386/kernel/apm.c
> @@ -540,12 +540,6 @@ static inline void apm_restore_cpus(cpum
>   * Also, we KNOW that for the non error case of apm_bios_call, there
>   * is no useful data returned in the low order 8 bits of eax.
>   */
> -#define APM_DO_CLI	\
> -	if (apm_info.allow_ints) \
> -		local_irq_enable(); \
> -	else \
> -		local_irq_disable();
> -
>  #ifdef APM_ZERO_SEGS
>  #	define APM_DECL_SEGS \
>  		unsigned int saved_fs; unsigned int saved_gs;
> @@ -583,11 +577,12 @@ static u8 apm_bios_call(u32 func, u32 eb
>  	u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, u32 *esi)
>  {
>  	APM_DECL_SEGS
> -	unsigned long		flags;
>  	cpumask_t		cpus;
>  	int			cpu;
>  	struct desc_struct	save_desc_40;
>  	struct desc_struct	*gdt;
> +	int			enable_irqs = 0;
> +	int			disable_irqs = 0;
>  
>  	cpus = apm_save_cpus();
>  	
> @@ -596,12 +591,26 @@ static u8 apm_bios_call(u32 func, u32 eb
>  	save_desc_40 = gdt[0x40 / 8];
>  	gdt[0x40 / 8] = bad_bios_desc;
>  
> -	local_save_flags(flags);
> -	APM_DO_CLI;
> +	if (apm_info.allow_ints) {
> +		if (irqs_disabled()) {
> +			local_irq_enable();
> +			disable_irqs = 1;
> +		}
> +	} else {
> +		if (!irqs_disabled()) {
> +			local_irq_disable();
> +			enable_irqs = 1;
> +		}
> +	}
> +
> +
>  	APM_DO_SAVE_SEGS;
>  	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
>  	APM_DO_RESTORE_SEGS;
> -	local_irq_restore(flags);
> +	if (disable_irqs)
> +		local_irq_disable();
> +	if (enable_irqs)
> +		local_irq_enable();
>  	gdt[0x40 / 8] = save_desc_40;
>  	put_cpu();
>  	apm_restore_cpus(cpus);
> @@ -627,11 +636,12 @@ static u8 apm_bios_call_simple(u32 func,
>  {
>  	u8			error;
>  	APM_DECL_SEGS
> -	unsigned long		flags;
>  	cpumask_t		cpus;
>  	int			cpu;
>  	struct desc_struct	save_desc_40;
>  	struct desc_struct	*gdt;
> +	int			enable_irqs = 0;
> +	int			disable_irqs = 0;
>  
>  	cpus = apm_save_cpus();
>  	
> @@ -640,12 +650,25 @@ static u8 apm_bios_call_simple(u32 func,
>  	save_desc_40 = gdt[0x40 / 8];
>  	gdt[0x40 / 8] = bad_bios_desc;
>  
> -	local_save_flags(flags);
> -	APM_DO_CLI;
> +	if (apm_info.allow_ints) {
> +		if (irqs_disabled()) {
> +			local_irq_enable();
> +			disable_irqs = 1;
> +		}
> +	} else {
> +		if (!irqs_disabled()) {
> +			local_irq_disable();
> +			enable_irqs = 1;
> +		}
> +	}
> +
>  	APM_DO_SAVE_SEGS;
>  	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
>  	APM_DO_RESTORE_SEGS;
> -	local_irq_restore(flags);
> +	if (disable_irqs)
> +		local_irq_disable();
> +	if (enable_irqs)
> +		local_irq_enable();
>  	gdt[0x40 / 8] = save_desc_40;
>  	put_cpu();
>  	apm_restore_cpus(cpus);
> _
> 

Re: [PATCH] lockdep: annotate i386 apm

[Andrew Morton]

On Thu, 12 Oct 2006 08:50:50 +0200
Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> Was my original _that_ hard to read?

The macro was bad enough.  Then you want an added another one and made it
reference a caller's local variable.  Another dummy-shaped dent in my wall.

I'd appreciate a fixed-up patch which changes the code's niceness in a
positive direction please - I'm obviously not cut out to work on apm.c.

Re: [PATCH] lockdep: annotate i386 apm

[Ingo Molnar]

* Andrew Morton <akpm@osdl.org> wrote:

> > So, say interrupts were enabled when entering apm_bios_call*(); you now
> > save that in flags, disable interrupts, and enable them again.
> > Upon reaching local_irq_restore(), we'll hit the else branch with irq's
> > enabled and call trace_hardirqs_on(), which goes EEEK!
> 
> I'd assumed lockdep was less stupid than that ;) This?  Seems a bit 
> overdone..

the problem is not lockdep but that the BIOS enables IRQs behind the 
back of the kernel. Lockdep needs to be taught about that - if this 
happens unconditionally then i'd suggest to insert an unconditional 
trace_hardirqs_on() call to after the local_irq_save() that we do prior 
calling the BIOS. (that will be a NOP if lockdep is not enabled)

	Ingo

[PATCH] lockdep: annotate i386 apm

[Peter Zijlstra]

Ok, so how about this:

---
Lockdep doesn't like to enable interrupts when they are enabled already.

BUG: warning at kernel/lockdep.c:1814/trace_hardirqs_on() (Not tainted)
 [<c04051ed>] show_trace_log_lvl+0x58/0x16a
 [<c04057fa>] show_trace+0xd/0x10
 [<c0405913>] dump_stack+0x19/0x1b
 [<c043abfb>] trace_hardirqs_on+0xa2/0x11e
 [<c041463c>] apm_bios_call_simple+0xcd/0xfd
 [<c0415242>] apm+0x92/0x5b1
 [<c0402005>] kernel_thread_helper+0x5/0xb
DWARF2 unwinder stuck at kernel_thread_helper+0x5/0xb
Leftover inexact backtrace:
 [<c04057fa>] show_trace+0xd/0x10
 [<c0405913>] dump_stack+0x19/0x1b
 [<c043abfb>] trace_hardirqs_on+0xa2/0x11e
 [<c041463c>] apm_bios_call_simple+0xcd/0xfd
 [<c0415242>] apm+0x92/0x5b1
 [<c0402005>] kernel_thread_helper+0x5/0xb

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 arch/i386/kernel/apm.c |   37 +++++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

Index: linux-2.6.18.noarch/arch/i386/kernel/apm.c
===================================================================
--- linux-2.6.18.noarch.orig/arch/i386/kernel/apm.c
+++ linux-2.6.18.noarch/arch/i386/kernel/apm.c
@@ -539,11 +539,30 @@ static inline void apm_restore_cpus(cpum
  * Also, we KNOW that for the non error case of apm_bios_call, there
  * is no useful data returned in the low order 8 bits of eax.
  */
-#define APM_DO_CLI	\
-	if (apm_info.allow_ints) \
-		local_irq_enable(); \
-	else \
+
+static inline unsigned long __apm_irq_save(void)
+{
+	unsigned long flags;
+	local_save_flags(flags);
+	if (apm_info.allow_ints) {
+		if (irqs_disabled_flags(flags))
+			local_irq_enable();
+	} else
+		local_irq_disable();
+
+	return flags;
+}
+
+#define apm_irq_save(flags) \
+	do { flags = __apm_irq_save(); } while (0)
+
+static inline void apm_irq_restore(unsigned long flags)
+{
+	if (irqs_disabled_flags(flags))
 		local_irq_disable();
+	else if (irqs_disabled())
+		local_irq_enable();
+}
 
 #ifdef APM_ZERO_SEGS
 #	define APM_DECL_SEGS \
@@ -595,12 +614,11 @@ static u8 apm_bios_call(u32 func, u32 eb
 	save_desc_40 = gdt[0x40 / 8];
 	gdt[0x40 / 8] = bad_bios_desc;
 
-	local_save_flags(flags);
-	APM_DO_CLI;
+	apm_irq_save(flags);
 	APM_DO_SAVE_SEGS;
 	apm_bios_call_asm(func, ebx_in, ecx_in, eax, ebx, ecx, edx, esi);
 	APM_DO_RESTORE_SEGS;
-	local_irq_restore(flags);
+	apm_irq_restore(flags);
 	gdt[0x40 / 8] = save_desc_40;
 	put_cpu();
 	apm_restore_cpus(cpus);
@@ -639,12 +657,11 @@ static u8 apm_bios_call_simple(u32 func,
 	save_desc_40 = gdt[0x40 / 8];
 	gdt[0x40 / 8] = bad_bios_desc;
 
-	local_save_flags(flags);
-	APM_DO_CLI;
+	apm_irq_save(flags);
 	APM_DO_SAVE_SEGS;
 	error = apm_bios_call_simple_asm(func, ebx_in, ecx_in, eax);
 	APM_DO_RESTORE_SEGS;
-	local_irq_restore(flags);
+	apm_irq_restore(flags);
 	gdt[0x40 / 8] = save_desc_40;
 	put_cpu();
 	apm_restore_cpus(cpus);

Re: [PATCH] lockdep: annotate i386 apm

[Peter Zijlstra]

On Thu, 2006-10-12 at 10:02 +0200, Ingo Molnar wrote:
> * Andrew Morton <akpm@osdl.org> wrote:
> 
> > > So, say interrupts were enabled when entering apm_bios_call*(); you now
> > > save that in flags, disable interrupts, and enable them again.
> > > Upon reaching local_irq_restore(), we'll hit the else branch with irq's
> > > enabled and call trace_hardirqs_on(), which goes EEEK!
> > 
> > I'd assumed lockdep was less stupid than that ;) This?  Seems a bit 
> > overdone..
> 
> the problem is not lockdep but that the BIOS enables IRQs behind the 
> back of the kernel. Lockdep needs to be taught about that - if this 
> happens unconditionally then i'd suggest to insert an unconditional 
> trace_hardirqs_on() call to after the local_irq_save() that we do prior 
> calling the BIOS. (that will be a NOP if lockdep is not enabled)

Well, its not quite like that, the irq mess in apm does an explicit
unbalanced irq action, and lockdep rightly triggers on that.
And adding to that comes the fact that we do indeed call a BIOS routine
which can do god knows what.

So we want to save irq state and force it into a known state; normally
it will only be disable - however in this case (when
apm_info.allow_ints) we force enable it. All end scope routines expect
irqs disabled.

logically it looks something like this

local_irq_save(flags)
local_irq_enable()
...
local_irq_disable() <--- missing
local_irq_restore(flags)

except that the first two statements are blended together to avoid the
unneeded disable.

The logic is sound because local_irq_restore will just set whatever was
saved, except lockdep gets confused by the unbalanced operations - a
good thing IMHO.