[PATCH] mm/shmem: Enclose shmem_mcopy_atomic_pte() with 'CONFIG_USERFAULTFD'

[SeongJae Park <sjpark@amazon.com>]

From: SeongJae Park <sjpark@amazon.de>

Commit 49eeab03fa0a ("userfaultfd: support minor fault handling for
shmem") introduced shmem_mcopy_atomic_pte().  The function is declared
in 'userfaultfd_k.h' when 'CONFIG_USERFAULTFD' is defined, and defined
as 'BUG()' if the config is unset.  However, the definition of the
function in 'shmem.c' is not protected by the '#ifdef' macro.  As a
result, the build fails when the config is not set.  This commit fixes
the problem.

Fixes: 49eeab03fa0a ("userfaultfd: support minor fault handling for shmem")
Signed-off-by: SeongJae Park <sjpark@amazon.de>

cr https://code.amazon.com/reviews/CR-47204463
---
 mm/shmem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index 547df2b766f7..c0d3abefeb3f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2359,6 +2359,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 	return inode;
 }
 
+#ifdef CONFIG_USERFAULTFD
 int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
 			   struct vm_area_struct *dst_vma,
 			   unsigned long dst_addr, unsigned long src_addr,
@@ -2492,6 +2493,7 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
 	shmem_inode_unacct_blocks(inode, 1);
 	goto out;
 }
+#endif
 
 #ifdef CONFIG_TMPFS
 static const struct inode_operations shmem_symlink_inode_operations;
-- 
2.17.1




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