From: Steven Rostedt rostedt@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@roeck-us.net Signed-off-by: Steven Rostedt rostedt@goodmis.org Signed-off-by: Arnd Bergmann arnd@arndb.de Acked-by: Russell King rmk+kernel@arm.linux.org.uk Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Andy Lutomirski luto@amacapital.net Cc: Andy Lutomirski luto@kernel.org Cc: Ard Biesheuvel ard.biesheuvel@linaro.org Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Borislav Petkov bp@suse.de Cc: Frederic Weisbecker fweisbec@gmail.com Cc: Jiri Olsa jolsa@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Mel Gorman mgorman@techsingularity.net Cc: Peter Zijlstra peterz@infradead.org Cc: Russell King - ARM Linux linux@armlinux.org.uk Cc: Stephane Eranian eranian@google.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vince Weaver vincent.weaver@maine.edu Cc: linux-arm-kernel@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@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org (cherry picked from commit c22d4b4d1c7fcc0d9eb4d8618d86c554c48ed9c0) Signed-off-by: Pavel Tatashin pasha.tatashin@oracle.com --- 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 9b32f76bb0dd..10f662498eb7 100644 --- 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_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) @@ -82,6 +83,7 @@ static inline void finish_arch_post_lock_switch(void) preempt_enable_no_resched(); } } +#endif /* !MODULE */
#endif /* CONFIG_MMU */