[PATCH] sched/core: don't include asm/mmu_context from drivers

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Arnd Bergmann]

The introduction of switch_mm_irqs_off() brought back an old bug
regarding the use of preempt_enable_no_resched:

As part of 62b94a08da1b ("sched/preempt: Take away
preempt_enable_no_resched() from modules"), the definition of
preempt_enable_no_resched() is only available in built-in code,
not in loadable modules, so we can't generally use it from header
files. However, the ARM version of finish_arch_post_lock_switch()
calls preempt_enable_no_resched() and is defined as a static
inline function in asm/mmu_context.h. This in turn means we cannot
include asm/mmu_context.h from modules.

With today's tip tree, asm/mmu_context.h gets included from
linux/mmu_context.h, which is normally the exact pattern one would
expect, but unfortunately, linux/mmu_context.h can be included from
the vhost driver that is a loadable module, now causing this compile
time error:

In file included from ../include/linux/mmu_context.h:4:0,
                 from ../drivers/vhost/vhost.c:18:
../arch/arm/include/asm/mmu_context.h: In function 'finish_arch_post_lock_switch':
../arch/arm/include/asm/mmu_context.h:88:3: error: implicit declaration of function 'preempt_enable_no_resched' [-Werror=implicit-function-declaration]
   preempt_enable_no_resched();

Andy already tried to fix the bug by including linux/preempt.h
from asm/mmu_context.h, but that obviously didn't help.

This reverts the earlier fix attempt and works around the problem
by including both linux/mmu_context.h and asm/mmu_context.h from
kernel/sched/core.c. This is not a good solution but seems less
hacky than the alternatives.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: f98db6013c55 ("sched/core: Add switch_mm_irqs_off() and use it in the scheduler")
Reverts: 88f10e37e150 ("sched/core, ARM: Include linux/preempt.h from asm/mmu_context.h")
---
 arch/arm/include/asm/mmu_context.h | 1 -
 include/linux/mmu_context.h        | 2 --
 kernel/sched/core.c                | 1 +
 3 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
index ed73babc0dc9..fa5b42d44985 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -15,7 +15,6 @@
 
 #include <linux/compiler.h>
 #include <linux/sched.h>
-#include <linux/preempt.h>
 #include <asm/cacheflush.h>
 #include <asm/cachetype.h>
 #include <asm/proc-fns.h>
diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index a4441784503b..88d270706792 100644
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -1,8 +1,6 @@
 #ifndef _LINUX_MMU_CONTEXT_H
 #define _LINUX_MMU_CONTEXT_H
 
-#include <asm/mmu_context.h>
-
 struct mm_struct;
 
 void use_mm(struct mm_struct *mm);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c82ca6eccfec..baa2a5152658 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -78,6 +78,7 @@
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
 #include <asm/irq_regs.h>
+#include <asm/mmu_context.h>
 #include <asm/mutex.h>
 #ifdef CONFIG_PARAVIRT
 #include <asm/paravirt.h>
-- 
2.7.0

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Arnd Bergmann]

The introduction of switch_mm_irqs_off() brought back an old bug
regarding the use of preempt_enable_no_resched:

As part of 62b94a08da1b ("sched/preempt: Take away
preempt_enable_no_resched() from modules"), the definition of
preempt_enable_no_resched() is only available in built-in code,
not in loadable modules, so we can't generally use it from header
files. However, the ARM version of finish_arch_post_lock_switch()
calls preempt_enable_no_resched() and is defined as a static
inline function in asm/mmu_context.h. This in turn means we cannot
include asm/mmu_context.h from modules.

With today's tip tree, asm/mmu_context.h gets included from
linux/mmu_context.h, which is normally the exact pattern one would
expect, but unfortunately, linux/mmu_context.h can be included from
the vhost driver that is a loadable module, now causing this compile
time error:

In file included from ../include/linux/mmu_context.h:4:0,
                 from ../drivers/vhost/vhost.c:18:
../arch/arm/include/asm/mmu_context.h: In function 'finish_arch_post_lock_switch':
../arch/arm/include/asm/mmu_context.h:88:3: error: implicit declaration of function 'preempt_enable_no_resched' [-Werror=implicit-function-declaration]
   preempt_enable_no_resched();

Andy already tried to fix the bug by including linux/preempt.h
from asm/mmu_context.h, but that obviously didn't help.

This reverts the earlier fix attempt and works around the problem
by including both linux/mmu_context.h and asm/mmu_context.h from
kernel/sched/core.c. This is not a good solution but seems less
hacky than the alternatives.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: f98db6013c55 ("sched/core: Add switch_mm_irqs_off() and use it in the scheduler")
Reverts: 88f10e37e150 ("sched/core, ARM: Include linux/preempt.h from asm/mmu_context.h")
---
 arch/arm/include/asm/mmu_context.h | 1 -
 include/linux/mmu_context.h        | 2 --
 kernel/sched/core.c                | 1 +
 3 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
index ed73babc0dc9..fa5b42d44985 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -15,7 +15,6 @@
 
 #include <linux/compiler.h>
 #include <linux/sched.h>
-#include <linux/preempt.h>
 #include <asm/cacheflush.h>
 #include <asm/cachetype.h>
 #include <asm/proc-fns.h>
diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index a4441784503b..88d270706792 100644
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -1,8 +1,6 @@
 #ifndef _LINUX_MMU_CONTEXT_H
 #define _LINUX_MMU_CONTEXT_H
 
-#include <asm/mmu_context.h>
-
 struct mm_struct;
 
 void use_mm(struct mm_struct *mm);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c82ca6eccfec..baa2a5152658 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -78,6 +78,7 @@
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
 #include <asm/irq_regs.h>
+#include <asm/mmu_context.h>
 #include <asm/mutex.h>
 #ifdef CONFIG_PARAVIRT
 #include <asm/paravirt.h>
-- 
2.7.0

Re: [PATCH] sched/core: don't include asm/mmu_context from drivers

[Steven Rostedt]

On Fri, 29 Apr 2016 10:52:32 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> This reverts the earlier fix attempt and works around the problem
> by including both linux/mmu_context.h and asm/mmu_context.h from
> kernel/sched/core.c. This is not a good solution but seems less
> hacky than the alternatives.

What about simply not compiling finish_arch_post_lock_switch() when
building modules?

(untested, not compiled or anything)

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
index fa5b42d44985..3f22d1b6bac8 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
 		cpu_switch_mm(mm->pgd, mm);
 }
 
+#ifndef MODULE
 #define finish_arch_post_lock_switch \
 	finish_arch_post_lock_switch
 static inline void finish_arch_post_lock_switch(void)
@@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
 		preempt_enable_no_resched();
 	}
 }
+#endif /* !MODULE */
 
 #endif	/* CONFIG_MMU */
 

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Steven Rostedt]

On Fri, 29 Apr 2016 10:52:32 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> This reverts the earlier fix attempt and works around the problem
> by including both linux/mmu_context.h and asm/mmu_context.h from
> kernel/sched/core.c. This is not a good solution but seems less
> hacky than the alternatives.

What about simply not compiling finish_arch_post_lock_switch() when
building modules?

(untested, not compiled or anything)

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
index fa5b42d44985..3f22d1b6bac8 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
 		cpu_switch_mm(mm->pgd, mm);
 }
 
+#ifndef MODULE
 #define finish_arch_post_lock_switch \
 	finish_arch_post_lock_switch
 static inline void finish_arch_post_lock_switch(void)
@@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
 		preempt_enable_no_resched();
 	}
 }
+#endif /* !MODULE */
 
 #endif	/* CONFIG_MMU */
 

Re: [PATCH] sched/core: don't include asm/mmu_context from drivers

[Arnd Bergmann]

On Friday 29 April 2016 09:42:18 Steven Rostedt wrote:
> On Fri, 29 Apr 2016 10:52:32 +0200
> Arnd Bergmann <arnd@arndb.de> wrote:
> 
> > This reverts the earlier fix attempt and works around the problem
> > by including both linux/mmu_context.h and asm/mmu_context.h from
> > kernel/sched/core.c. This is not a good solution but seems less
> > hacky than the alternatives.
> 
> What about simply not compiling finish_arch_post_lock_switch() when
> building modules?
> 
> (untested, not compiled or anything)
> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> 

It should work as well.

I think I suggested doing that the last time the problem came up
a few years ago, but we ended up not including the header instead,
so I kept doing that.

	Arnd

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Arnd Bergmann]

On Friday 29 April 2016 09:42:18 Steven Rostedt wrote:
> On Fri, 29 Apr 2016 10:52:32 +0200
> Arnd Bergmann <arnd@arndb.de> wrote:
> 
> > This reverts the earlier fix attempt and works around the problem
> > by including both linux/mmu_context.h and asm/mmu_context.h from
> > kernel/sched/core.c. This is not a good solution but seems less
> > hacky than the alternatives.
> 
> What about simply not compiling finish_arch_post_lock_switch() when
> building modules?
> 
> (untested, not compiled or anything)
> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> 

It should work as well.

I think I suggested doing that the last time the problem came up
a few years ago, but we ended up not including the header instead,
so I kept doing that.

	Arnd

Re: [PATCH] sched/core: don't include asm/mmu_context from drivers

[Andy Lutomirski]

On Fri, Apr 29, 2016 at 8:37 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Friday 29 April 2016 09:42:18 Steven Rostedt wrote:
>> On Fri, 29 Apr 2016 10:52:32 +0200
>> Arnd Bergmann <arnd@arndb.de> wrote:
>>
>> > This reverts the earlier fix attempt and works around the problem
>> > by including both linux/mmu_context.h and asm/mmu_context.h from
>> > kernel/sched/core.c. This is not a good solution but seems less
>> > hacky than the alternatives.
>>
>> What about simply not compiling finish_arch_post_lock_switch() when
>> building modules?
>>
>> (untested, not compiled or anything)
>>
>> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
>>
>
> It should work as well.
>
> I think I suggested doing that the last time the problem came up
> a few years ago, but we ended up not including the header instead,
> so I kept doing that.
>
>         Arnd

This variant looks considerably nicer to me.

--Andy

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Andy Lutomirski]

On Fri, Apr 29, 2016 at 8:37 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Friday 29 April 2016 09:42:18 Steven Rostedt wrote:
>> On Fri, 29 Apr 2016 10:52:32 +0200
>> Arnd Bergmann <arnd@arndb.de> wrote:
>>
>> > This reverts the earlier fix attempt and works around the problem
>> > by including both linux/mmu_context.h and asm/mmu_context.h from
>> > kernel/sched/core.c. This is not a good solution but seems less
>> > hacky than the alternatives.
>>
>> What about simply not compiling finish_arch_post_lock_switch() when
>> building modules?
>>
>> (untested, not compiled or anything)
>>
>> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
>>
>
> It should work as well.
>
> I think I suggested doing that the last time the problem came up
> a few years ago, but we ended up not including the header instead,
> so I kept doing that.
>
>         Arnd

This variant looks considerably nicer to me.

--Andy

Re: [PATCH] sched/core: don't include asm/mmu_context from drivers

[Andy Lutomirski]

On Fri, Apr 29, 2016 at 6:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 29 Apr 2016 10:52:32 +0200
> Arnd Bergmann <arnd@arndb.de> wrote:
>
>> This reverts the earlier fix attempt and works around the problem
>> by including both linux/mmu_context.h and asm/mmu_context.h from
>> kernel/sched/core.c. This is not a good solution but seems less
>> hacky than the alternatives.
>
> What about simply not compiling finish_arch_post_lock_switch() when
> building modules?
>
> (untested, not compiled or anything)
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
> index fa5b42d44985..3f22d1b6bac8 100644
> --- a/arch/arm/include/asm/mmu_context.h
> +++ b/arch/arm/include/asm/mmu_context.h
> @@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
>                 cpu_switch_mm(mm->pgd, mm);
>  }
>
> +#ifndef MODULE
>  #define finish_arch_post_lock_switch \
>         finish_arch_post_lock_switch
>  static inline void finish_arch_post_lock_switch(void)
> @@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
>                 preempt_enable_no_resched();
>         }
>  }
> +#endif /* !MODULE */
>
>  #endif /* CONFIG_MMU */
>


Can someone in arm land ack this so Ingo can apply it?

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Andy Lutomirski]

On Fri, Apr 29, 2016 at 6:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 29 Apr 2016 10:52:32 +0200
> Arnd Bergmann <arnd@arndb.de> wrote:
>
>> This reverts the earlier fix attempt and works around the problem
>> by including both linux/mmu_context.h and asm/mmu_context.h from
>> kernel/sched/core.c. This is not a good solution but seems less
>> hacky than the alternatives.
>
> What about simply not compiling finish_arch_post_lock_switch() when
> building modules?
>
> (untested, not compiled or anything)
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
> index fa5b42d44985..3f22d1b6bac8 100644
> --- a/arch/arm/include/asm/mmu_context.h
> +++ b/arch/arm/include/asm/mmu_context.h
> @@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
>                 cpu_switch_mm(mm->pgd, mm);
>  }
>
> +#ifndef MODULE
>  #define finish_arch_post_lock_switch \
>         finish_arch_post_lock_switch
>  static inline void finish_arch_post_lock_switch(void)
> @@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
>                 preempt_enable_no_resched();
>         }
>  }
> +#endif /* !MODULE */
>
>  #endif /* CONFIG_MMU */
>


Can someone in arm land ack this so Ingo can apply it?

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC

Re: [PATCH] sched/core: don't include asm/mmu_context from drivers

[Russell King - ARM Linux]

On Thu, May 12, 2016 at 10:46:56PM -0700, Andy Lutomirski wrote:
> On Fri, Apr 29, 2016 at 6:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Fri, 29 Apr 2016 10:52:32 +0200
> > Arnd Bergmann <arnd@arndb.de> wrote:
> >
> >> This reverts the earlier fix attempt and works around the problem
> >> by including both linux/mmu_context.h and asm/mmu_context.h from
> >> kernel/sched/core.c. This is not a good solution but seems less
> >> hacky than the alternatives.
> >
> > What about simply not compiling finish_arch_post_lock_switch() when
> > building modules?
> >
> > (untested, not compiled or anything)
> >
> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> > ---
> > diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
> > index fa5b42d44985..3f22d1b6bac8 100644
> > --- a/arch/arm/include/asm/mmu_context.h
> > +++ b/arch/arm/include/asm/mmu_context.h
> > @@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
> >                 cpu_switch_mm(mm->pgd, mm);
> >  }
> >
> > +#ifndef MODULE
> >  #define finish_arch_post_lock_switch \
> >         finish_arch_post_lock_switch
> >  static inline void finish_arch_post_lock_switch(void)
> > @@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
> >                 preempt_enable_no_resched();
> >         }
> >  }
> > +#endif /* !MODULE */
> >
> >  #endif /* CONFIG_MMU */
> >
> 
> 
> Can someone in arm land ack this so Ingo can apply it?

Sorry, I'm simply unable to read every message that comes in.

Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Russell King - ARM Linux]

On Thu, May 12, 2016 at 10:46:56PM -0700, Andy Lutomirski wrote:
> On Fri, Apr 29, 2016 at 6:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Fri, 29 Apr 2016 10:52:32 +0200
> > Arnd Bergmann <arnd@arndb.de> wrote:
> >
> >> This reverts the earlier fix attempt and works around the problem
> >> by including both linux/mmu_context.h and asm/mmu_context.h from
> >> kernel/sched/core.c. This is not a good solution but seems less
> >> hacky than the alternatives.
> >
> > What about simply not compiling finish_arch_post_lock_switch() when
> > building modules?
> >
> > (untested, not compiled or anything)
> >
> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> > ---
> > diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
> > index fa5b42d44985..3f22d1b6bac8 100644
> > --- a/arch/arm/include/asm/mmu_context.h
> > +++ b/arch/arm/include/asm/mmu_context.h
> > @@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
> >                 cpu_switch_mm(mm->pgd, mm);
> >  }
> >
> > +#ifndef MODULE
> >  #define finish_arch_post_lock_switch \
> >         finish_arch_post_lock_switch
> >  static inline void finish_arch_post_lock_switch(void)
> > @@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
> >                 preempt_enable_no_resched();
> >         }
> >  }
> > +#endif /* !MODULE */
> >
> >  #endif /* CONFIG_MMU */
> >
> 
> 
> Can someone in arm land ack this so Ingo can apply it?

Sorry, I'm simply unable to read every message that comes in.

Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

Re: [PATCH] sched/core: don't include asm/mmu_context from drivers

[Arnd Bergmann]

On Thursday 12 May 2016 22:46:56 Andy Lutomirski wrote:
> On Fri, Apr 29, 2016 at 6:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Fri, 29 Apr 2016 10:52:32 +0200
> > Arnd Bergmann <arnd@arndb.de> wrote:
> >
> >> This reverts the earlier fix attempt and works around the problem
> >> by including both linux/mmu_context.h and asm/mmu_context.h from
> >> kernel/sched/core.c. This is not a good solution but seems less
> >> hacky than the alternatives.
> >
> > What about simply not compiling finish_arch_post_lock_switch() when
> > building modules?
> >
> > (untested, not compiled or anything)
> >
> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> > ---
> > diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
> > index fa5b42d44985..3f22d1b6bac8 100644
> > --- a/arch/arm/include/asm/mmu_context.h
> > +++ b/arch/arm/include/asm/mmu_context.h
> > @@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
> >                 cpu_switch_mm(mm->pgd, mm);
> >  }
> >
> > +#ifndef MODULE
> >  #define finish_arch_post_lock_switch \
> >         finish_arch_post_lock_switch
> >  static inline void finish_arch_post_lock_switch(void)
> > @@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
> >                 preempt_enable_no_resched();
> >         }
> >  }
> > +#endif /* !MODULE */
> >
> >  #endif /* CONFIG_MMU */
> >
> 
> 
> Can someone in arm land ack this so Ingo can apply it?
> 

Sorry I forgot about this when I had my original patch in the
randconfig patch stack. I've reverted this now and am testing
with Steve's version. If I see no other regressions, I'll resend
this with a proper changelog and Russell's Ack.

	Arnd

[PATCH] sched/core: don't include asm/mmu_context from drivers

[Arnd Bergmann]

On Thursday 12 May 2016 22:46:56 Andy Lutomirski wrote:
> On Fri, Apr 29, 2016 at 6:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Fri, 29 Apr 2016 10:52:32 +0200
> > Arnd Bergmann <arnd@arndb.de> wrote:
> >
> >> This reverts the earlier fix attempt and works around the problem
> >> by including both linux/mmu_context.h and asm/mmu_context.h from
> >> kernel/sched/core.c. This is not a good solution but seems less
> >> hacky than the alternatives.
> >
> > What about simply not compiling finish_arch_post_lock_switch() when
> > building modules?
> >
> > (untested, not compiled or anything)
> >
> > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> > ---
> > diff --git a/arch/arm/include/asm/mmu_context.h b/arch/arm/include/asm/mmu_context.h
> > index fa5b42d44985..3f22d1b6bac8 100644
> > --- a/arch/arm/include/asm/mmu_context.h
> > +++ b/arch/arm/include/asm/mmu_context.h
> > @@ -66,6 +66,7 @@ static inline void check_and_switch_context(struct mm_struct *mm,
> >                 cpu_switch_mm(mm->pgd, mm);
> >  }
> >
> > +#ifndef MODULE
> >  #define finish_arch_post_lock_switch \
> >         finish_arch_post_lock_switch
> >  static inline void finish_arch_post_lock_switch(void)
> > @@ -87,6 +88,7 @@ static inline void finish_arch_post_lock_switch(void)
> >                 preempt_enable_no_resched();
> >         }
> >  }
> > +#endif /* !MODULE */
> >
> >  #endif /* CONFIG_MMU */
> >
> 
> 
> Can someone in arm land ack this so Ingo can apply it?
> 

Sorry I forgot about this when I had my original patch in the
randconfig patch stack. I've reverted this now and am testing
with Steve's version. If I see no other regressions, I'll resend
this with a proper changelog and Russell's Ack.

	Arnd