Re: [PATCH v2] mm/kmemleak: Use explicit cast to cast pointer from percpu to generic AS

[Uros Bizjak <ubizjak@gmail.com>]

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On Sun, Aug 18, 2024 at 5:26 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> Use explicit cast to cast pointer from percpu to generic address space.
>
> The patch will avoid future build errors due to pointer address
> space mismatch with enabled strict percpu address space checks.
>
> The patch also fixes following sparse warnings:
>
> kmemleak.c:1063:39: warning: cast removes address space '__percpu' of expression
> kmemleak.c:1138:37: warning: cast removes address space '__percpu' of expression
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>

Actually, we can do something around the lines of the attached patch
and still keep the __must_check directive active.

Please disregard this patch, a new (better) approach is in the works.

Uros.

> ---
> v2: Use explicit casts instead of IS_ERR_PCPU().
> ---
>  mm/kmemleak.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 764b08100570..fc2e09ec48f8 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1059,8 +1059,9 @@ void __ref kmemleak_alloc_percpu(const void __percpu *ptr, size_t size,
>          * Percpu allocations are only scanned and not reported as leaks
>          * (min_count is set to 0).
>          */
> -       if (kmemleak_enabled && ptr && !IS_ERR(ptr))
> -               create_object_percpu((unsigned long)ptr, size, 0, gfp);
> +       if (kmemleak_enabled && ptr &&
> +           !IS_ERR((const void *)(__force const unsigned long)ptr))
> +               create_object_percpu((__force unsigned long)ptr, size, 0, gfp);
>  }
>  EXPORT_SYMBOL_GPL(kmemleak_alloc_percpu);
>
> @@ -1134,8 +1135,9 @@ void __ref kmemleak_free_percpu(const void __percpu *ptr)
>  {
>         pr_debug("%s(0x%px)\n", __func__, ptr);
>
> -       if (kmemleak_free_enabled && ptr && !IS_ERR(ptr))
> -               delete_object_full((unsigned long)ptr, OBJECT_PERCPU);
> +       if (kmemleak_free_enabled && ptr &&
> +           !IS_ERR((const void *)(__force const unsigned long)ptr))
> +               delete_object_full((__force unsigned long)ptr, OBJECT_PERCPU);
>  }
>  EXPORT_SYMBOL_GPL(kmemleak_free_percpu);
>
> --
> 2.42.0
>

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diff --git a/include/linux/err.h b/include/linux/err.h
index b5d9bb2a2349..6dd7f00d422d 100644
--- a/include/linux/err.h
+++ b/include/linux/err.h
@@ -41,6 +41,8 @@ static inline void * __must_check ERR_PTR(long error)
 	return (void *) error;
 }
 
+#define ERR_PTR_PCPU(ptr) ({ (void __percpu *)(unsigned long)ERR_PTR(ptr); })
+
 /**
  * PTR_ERR - Extract the error code from an error pointer.
  * @ptr: An error pointer.
@@ -51,6 +53,8 @@ static inline long __must_check PTR_ERR(__force const void *ptr)
 	return (long) ptr;
 }
 
+#define PTR_ERR_PCPU(ptr) ({ PTR_ERR((void *)(__force unsigned long)ptr); })
+
 /**
  * IS_ERR - Detect an error pointer.
  * @ptr: The pointer to check.
@@ -61,6 +65,8 @@ static inline bool __must_check IS_ERR(__force const void *ptr)
 	return IS_ERR_VALUE((unsigned long)ptr);
 }
 
+#define IS_ERR_PCPU(ptr) ({ IS_ERR((void *)(__force unsigned long)ptr); })
+
 /**
  * IS_ERR_OR_NULL - Detect an error pointer or a null pointer.
  * @ptr: The pointer to check.