arch: fix has_transparent_hugepage()

I've just discovered that the useful-sounding has_transparent_hugepage()
is actually an architecture-dependent minefield: on some arches it only
builds if CONFIG_TRANSPARENT_HUGEPAGE=y, on others it's also there when
not, but on some of those (arm and arm64) it then gives the wrong
answer; and on mips alone it's marked __init, which would crash if
called later (but so far it has not been called later).

Straighten this out: make it available to all configs, with a sensible
default in asm-generic/pgtable.h, removing its definitions from those
arches (arc, arm, arm64, sparc, tile) which are served by the default,
adding #define has_transparent_hugepage has_transparent_hugepage to
those (mips, powerpc, s390, x86) which need to override the default at
runtime, and removing the __init from mips (but maybe that kind of code
should be avoided after init: set a static variable the first time it's
called).

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Yang Shi <yang.shi@linaro.org>
Cc: Ning Qu <quning@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Vineet Gupta <vgupta@synopsys.com>		[arch/arc]
Acked-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>	[arch/s390]
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 10 deletions

diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 9a4fe0133ff1..f53a7e3a4dd9 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -468,6 +468,7 @@ static inline int io_remap_pfn_range(struct vm_area_struct *vma,
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 
+#define has_transparent_hugepage has_transparent_hugepage
 extern int has_transparent_hugepage(void);
 
 static inline int pmd_trans_huge(pmd_t pmd)
diff --git a/arch/mips/mm/tlb-r4k.c b/arch/mips/mm/tlb-r4k.c
index c17d7627f872..2d93b63cf830 100644
--- a/arch/mips/mm/tlb-r4k.c
+++ b/arch/mips/mm/tlb-r4k.c
@@ -400,19 +400,20 @@ void add_wired_entry(unsigned long entrylo0, unsigned long entrylo1,
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 
-int __init has_transparent_hugepage(void)
+int has_transparent_hugepage(void)
 {
-	unsigned int mask;
-	unsigned long flags;
-
-	local_irq_save(flags);
-	write_c0_pagemask(PM_HUGE_MASK);
-	back_to_back_c0_hazard();
-	mask = read_c0_pagemask();
-	write_c0_pagemask(PM_DEFAULT_MASK);
+	static unsigned int mask = -1;
 
-	local_irq_restore(flags);
+	if (mask == -1) {	/* first call comes during __init */
+		unsigned long flags;
 
+		local_irq_save(flags);
+		write_c0_pagemask(PM_HUGE_MASK);
+		back_to_back_c0_hazard();
+		mask = read_c0_pagemask();
+		write_c0_pagemask(PM_DEFAULT_MASK);
+		local_irq_restore(flags);
+	}
 	return mask == PM_HUGE_MASK;
 }