2023-04-05 10:39:30

by Steven Price

Subject: [PATCH v2] smaps: Fix defined but not used smaps_shmem_walk_ops

When !CONFIG_SHMEM smaps_shmem_walk_ops is defined but not used,
triggering a compiler warning. To avoid the warning remove the #ifdef
around the usage. This has no effect because shmem_mapping() is a stub
returning false when !CONFIG_SHMEM so the code will be compiled out,
however we now need to also provide a stub for shmem_swap_usage().

Fixes: 7b86ac3371b7 ("pagewalk: separate function pointers from iterator data")
Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Steven Price <[email protected]>
---
I've implemented Jason's suggestion of removing the #ifdef around the
usage and prodiving a stub for shmem_swap_usage() instead.

fs/proc/task_mmu.c | 3 +--
include/linux/shmem_fs.h | 7 +++++++
2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 6a96e1713fd5..cb49479acd2e 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -782,7 +782,6 @@ static void smap_gather_stats(struct vm_area_struct *vma,
if (start >= vma->vm_end)
return;

-#ifdef CONFIG_SHMEM
if (vma->vm_file && shmem_mapping(vma->vm_file->f_mapping)) {
/*
* For shared or readonly shmem mappings we know that all
@@ -803,7 +802,7 @@ static void smap_gather_stats(struct vm_area_struct *vma,
ops = &smaps_shmem_walk_ops;
}
}
-#endif
+
/* mmap_lock is held in m_start */
if (!start)
walk_page_vma(vma, ops, mss);
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 103d1000a5a2..762c37b32bd4 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -94,7 +94,14 @@ int shmem_unuse(unsigned int type);

extern bool shmem_is_huge(struct inode *inode, pgoff_t index, bool shmem_huge_force,
struct mm_struct *mm, unsigned long vm_flags);
+#ifdef CONFIG_SHMEM
extern unsigned long shmem_swap_usage(struct vm_area_struct *vma);
+#else
+static inline unsigned long shmem_swap_usage(struct vm_area_struct *vma)
+{
+ return 0;
+}
+#endif
extern unsigned long shmem_partial_swap_usage(struct address_space *mapping,
pgoff_t start, pgoff_t end);

--
2.34.1

2023-04-05 12:16:45

by Jason Gunthorpe

Subject: Re: [PATCH v2] smaps: Fix defined but not used smaps_shmem_walk_ops

On Wed, Apr 05, 2023 at 11:38:19AM +0100, Steven Price wrote:
> When !CONFIG_SHMEM smaps_shmem_walk_ops is defined but not used,
> triggering a compiler warning. To avoid the warning remove the #ifdef
> around the usage. This has no effect because shmem_mapping() is a stub
> returning false when !CONFIG_SHMEM so the code will be compiled out,
> however we now need to also provide a stub for shmem_swap_usage().
>
> Fixes: 7b86ac3371b7 ("pagewalk: separate function pointers from iterator data")
> Reported-by: kernel test robot <[email protected]>
> Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/
> Signed-off-by: Steven Price <[email protected]>
> ---
> I've implemented Jason's suggestion of removing the #ifdef around the
> usage and prodiving a stub for shmem_swap_usage() instead.

This seems OK

Reviewed-by: Jason Gunthorpe <[email protected]>


> extern bool shmem_is_huge(struct inode *inode, pgoff_t index, bool shmem_huge_force,
> struct mm_struct *mm, unsigned long vm_flags);
> +#ifdef CONFIG_SHMEM
> extern unsigned long shmem_swap_usage(struct vm_area_struct *vma);
> +#else
> +static inline unsigned long shmem_swap_usage(struct vm_area_struct *vma)
> +{
> + return 0;
> +}
> +#endif

Though it would be nice if this file didn't have so many ifdef blocks

Jason