sparc64: Fix kernel panic due to erroneous #ifdef surrounding pmd_write()

This commit moves sparc64's prototype of pmd_write() outside
of the CONFIG_TRANSPARENT_HUGEPAGE ifdef.

In 2013, commit a7b9403f ("sparc64: Encode huge PMDs using PTE
encoding.") exposed a path where pmd_write() could be called without
CONFIG_TRANSPARENT_HUGEPAGE defined.  This can result in the panic below.

The diff is awkward to read, but the changes are straightforward.
pmd_write() was moved outside of #ifdef CONFIG_TRANSPARENT_HUGEPAGE.
Also, __HAVE_ARCH_PMD_WRITE was defined.

kernel BUG at include/asm-generic/pgtable.h:576!
              \|/ ____ \|/
              "@'/ .. \`@"
              /_| \__/ |_\
                 \__U_/
oracle_8114_cdb(8114): Kernel bad sw trap 5 [#1]
CPU: 120 PID: 8114 Comm: oracle_8114_cdb Not tainted
4.1.12-61.7.1.el6uek.rc1.sparc64 #1
task: fff8400700a24d60 ti: fff8400700bc4000 task.ti: fff8400700bc4000
TSTATE: 0000004411e01607 TPC: 00000000004609f8 TNPC: 00000000004609fc Y:
00000005    Not tainted
TPC: <gup_huge_pmd+0x198/0x1e0>
g0: 000000000001c000 g1: 0000000000ef3954 g2: 0000000000000000 g3: 0000000000000001
g4: fff8400700a24d60 g5: fff8001fa5c10000 g6: fff8400700bc4000 g7: 0000000000000720
o0: 0000000000bc5058 o1: 0000000000000240 o2: 0000000000006000 o3: 0000000000001c00
o4: 0000000000000000 o5: 0000048000080000 sp: fff8400700bc6ab1 ret_pc: 00000000004609f0
RPC: <gup_huge_pmd+0x190/0x1e0>
l0: fff8400700bc74fc l1: 0000000000020000 l2: 0000000000002000 l3: 0000000000000000
l4: fff8001f93250950 l5: 000000000113f800 l6: 0000000000000004 l7: 0000000000000000
i0: fff8400700ca46a0 i1: bd0000085e800453 i2: 000000026a0c4000 i3: 000000026a0c6000
i4: 0000000000000001 i5: fff800070c958de8 i6: fff8400700bc6b61 i7: 0000000000460dd0
I7: <gup_pud_range+0x170/0x1a0>
Call Trace:
 [0000000000460dd0] gup_pud_range+0x170/0x1a0
 [0000000000460e84] get_user_pages_fast+0x84/0x120
 [00000000006f5a18] iov_iter_get_pages+0x98/0x240
 [00000000005fa744] do_direct_IO+0xf64/0x1e00
 [00000000005fbbc0] __blockdev_direct_IO+0x360/0x15a0
 [00000000101f74fc] ext4_ind_direct_IO+0xdc/0x400 [ext4]
 [00000000101af690] ext4_ext_direct_IO+0x1d0/0x2c0 [ext4]
 [00000000101af86c] ext4_direct_IO+0xec/0x220 [ext4]
 [0000000000553bd4] generic_file_read_iter+0x114/0x140
 [00000000005bdc2c] __vfs_read+0xac/0x100
 [00000000005bf254] vfs_read+0x54/0x100
 [00000000005bf368] SyS_pread64+0x68/0x80
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/include/asm/pgtable_64.h

@@ -679,26 +679,27 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
 	return pte_pfn(pte);
 }
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-static inline unsigned long pmd_dirty(pmd_t pmd)
+#define __HAVE_ARCH_PMD_WRITE
+static inline unsigned long pmd_write(pmd_t pmd)
 {
 	pte_t pte = __pte(pmd_val(pmd));
 
-	return pte_dirty(pte);
+	return pte_write(pte);
 }
 
-static inline unsigned long pmd_young(pmd_t pmd)
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline unsigned long pmd_dirty(pmd_t pmd)
 {
 	pte_t pte = __pte(pmd_val(pmd));
 
-	return pte_young(pte);
+	return pte_dirty(pte);
 }
 
-static inline unsigned long pmd_write(pmd_t pmd)
+static inline unsigned long pmd_young(pmd_t pmd)
 {
 	pte_t pte = __pte(pmd_val(pmd));
 
-	return pte_write(pte);
+	return pte_young(pte);
 }
 
 static inline unsigned long pmd_trans_huge(pmd_t pmd)