[PATCH 4.4 13/78] ARM: Hide finish_arch_post_lock_switch() from modules

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Steven Rostedt <rostedt at goodmis.org>

commit ef0491ea17f8019821c7e9c8e801184ecf17f85a upstream.

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 with modular configs:

  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. Arnd suggested reordering
the header files, which wasn't popular, so let's use 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.

Tested-by: Guenter Roeck <linux at roeck-us.net>
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: Russell King <rmk+kernel at arm.linux.org.uk>
Cc: Alexander Shishkin <alexander.shishkin at linux.intel.com>
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Cc: Arnaldo Carvalho de Melo <acme at redhat.com>
Cc: Borislav Petkov <bp at suse.de>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Jiri Olsa <jolsa at redhat.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Russell King - ARM Linux <linux at armlinux.org.uk>
Cc: Stephane Eranian <eranian at google.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Vince Weaver <vincent.weaver at maine.edu>
Cc: linux-arm-kernel at lists.infradead.org
Fixes: f98db6013c55 ("sched/core: Add switch_mm_irqs_off() and use it in the scheduler")
Link: http://lkml.kernel.org/r/1463146234-161304-1-git-send-email-arnd@arndb.de
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

---
 arch/arm/include/asm/mmu_context.h |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/arm/include/asm/mmu_context.h
+++ b/arch/arm/include/asm/mmu_context.h
@@ -61,6 +61,7 @@ static inline void check_and_switch_cont
 		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)
@@ -82,6 +83,7 @@ static inline void finish_arch_post_lock
 		preempt_enable_no_resched();
 	}
 }
+#endif /* !MODULE */
 
 #endif	/* CONFIG_MMU */