[PATCH] smaps: Fix defined but not used smaps_shmem_walk_ops

[PATCH] smaps: Fix defined but not used smaps_shmem_walk_ops

[Steven Price]

When !CONFIG_SHMEM smaps_shmem_walk_ops is defined but not used,
triggering a compiler warning. Surround the definition with an #ifdef to
keep the compiler happy.

Fixes: 7b86ac3371b7 ("pagewalk: separate function pointers from iterator data")
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202304031749.UiyJpxzF-lkp@intel.com/
Signed-off-by: Steven Price <steven.price@arm.com>
---
 fs/proc/task_mmu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 6a96e1713fd5..3d4f8859dac1 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -761,11 +761,13 @@ static const struct mm_walk_ops smaps_walk_ops = {
 	.hugetlb_entry		= smaps_hugetlb_range,
 };
 
+#ifdef CONFIG_SHMEM
 static const struct mm_walk_ops smaps_shmem_walk_ops = {
 	.pmd_entry		= smaps_pte_range,
 	.hugetlb_entry		= smaps_hugetlb_range,
 	.pte_hole		= smaps_pte_hole,
 };
+#endif
 
 /*
  * Gather mem stats from @vma with the indicated beginning
-- 
2.34.1

Re: [PATCH] smaps: Fix defined but not used smaps_shmem_walk_ops

[Jason Gunthorpe]

On Mon, Apr 03, 2023 at 12:12:55PM +0100, Steven Price wrote:
> When !CONFIG_SHMEM smaps_shmem_walk_ops is defined but not used,
> triggering a compiler warning. Surround the definition with an #ifdef to
> keep the compiler happy.
> 
> Fixes: 7b86ac3371b7 ("pagewalk: separate function pointers from iterator data")
> Reported-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/oe-kbuild-all/202304031749.UiyJpxzF-lkp@intel.com/
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
>  fs/proc/task_mmu.c | 2 ++
>  1 file changed, 2 insertions(+)

I think it would be better to enclose the definition of
shmem_swap_usage() in its header with a stub like shmem_mapping and
remove the ifdef completely. shmem_mapping() is already compile time
false.

#ifdef CONFIG_SHMEM
        if (vma->vm_file && shmem_mapping(vma->vm_file->f_mapping)) {
                /*
                 * For shared or readonly shmem mappings we know that all
                 * swapped out pages belong to the shmem object, and we can
                 * obtain the swap value much more efficiently. For private
                 * writable mappings, we might have COW pages that are
                 * not affected by the parent swapped out pages of the shmem
                 * object, so we have to distinguish them during the page walk.
                 * Unless we know that the shmem object (or the part mapped by
                 * our VMA) has no swapped out pages at all.
                 */
                unsigned long shmem_swapped = shmem_swap_usage(vma);

                if (!start && (!shmem_swapped || (vma->vm_flags & VM_SHARED) ||
                                        !(vma->vm_flags & VM_WRITE))) {
                        mss->swap += shmem_swapped;
                } else {
                        ops = &smaps_shmem_walk_ops;
                }
        }
#endif


Jason