linux-kernel - [tip:sched/core] ARM: Hide finish_arch_post_lock

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Date:	Fri, 13 May 2016 07:15:39 -0700
From:	tip-bot for Steven Rostedt <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, eranian@...gle.com, acme@...hat.com,
	tglx@...utronix.de, alexander.shishkin@...ux.intel.com, bp@...e.de,
	ard.biesheuvel@...aro.org, rostedt@...dmis.org, hpa@...or.com,
	mingo@...nel.org, jolsa@...hat.com, arnd@...db.de,
	linux@...ck-us.net, luto@...nel.org, linux@...linux.org.uk,
	vincent.weaver@...ne.edu, rmk+kernel@....linux.org.uk,
	fweisbec@...il.com, luto@...capital.net,
	mgorman@...hsingularity.net, linux-kernel@...r.kernel.org,
	peterz@...radead.org
Subject: [tip:sched/core] ARM: Hide finish_arch_post_lock_switch() from
 modules

Commit-ID:  ef0491ea17f8019821c7e9c8e801184ecf17f85a
Gitweb:     http://git.kernel.org/tip/ef0491ea17f8019821c7e9c8e801184ecf17f85a
Author:     Steven Rostedt <rostedt@...dmis.org>
AuthorDate: Fri, 13 May 2016 15:30:13 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 13 May 2016 16:12:53 +0200

ARM: Hide finish_arch_post_lock_switch() from modules

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@...ck-us.net>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Acked-by: Russell King <rmk+kernel@....linux.org.uk>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Russell King - ARM Linux <linux@...linux.org.uk>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: linux-arm-kernel@...ts.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@...nel.org>
---
 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 ed73bab..3cc14dd 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 */