From: Steven Rostedt <rost...@goodmis.org>
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 didn't help. I suggested reordering
the header files, which wasn't popular, but Steve came up with this
workaround instead:
The finish_arch_post_lock_switch() definition is now also hidden
inside of #ifdef MODULE, so we don't see anything referencing
preempt_enable_no_resched() from a header file. I've built a
few hundred randconfig kernels with this, and did not see any
new problems.
Fixes: f98db6013c55 ("sched/core: Add switch_mm_irqs_off() and use it in the
scheduler")
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Arnd Bergmann <a...@arndb.de>
Acked-by: Russell King <rmk+ker...@arm.linux.org.uk>
---
arch/arm/include/asm/mmu_context.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/arm/include/asm/mmu_context.h
b/arch/arm/include/asm/mmu_context.h
index ed73babc0dc9..3cc14dd8587c 100644
--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -67,6 +67,7 @@ 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)
@@ -88,6 +89,7 @@ static inline void finish_arch_post_lock_switch(void)
preempt_enable_no_resched();
}
}
+#endif /* !MODULE */
#endif /* CONFIG_MMU */
--
2.7.0
