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 <[email protected]>
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
On Fri, 29 Apr 2016 10:52:32 +0200
Arnd Bergmann <[email protected]> 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 <[email protected]>
---
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 */
On Friday 29 April 2016 09:42:18 Steven Rostedt wrote:
> On Fri, 29 Apr 2016 10:52:32 +0200
> Arnd Bergmann <[email protected]> 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 <[email protected]>
>
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
On Fri, Apr 29, 2016 at 8:37 AM, Arnd Bergmann <[email protected]> wrote:
> On Friday 29 April 2016 09:42:18 Steven Rostedt wrote:
>> On Fri, 29 Apr 2016 10:52:32 +0200
>> Arnd Bergmann <[email protected]> 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 <[email protected]>
>>
>
> 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