Hello,
On Sat, Oct 07, 2023 at 09:51:01PM +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> Introduce alloc_size_percpu() to get the size of the dynamic per-cpu
> area. It will be used by bpf memory allocator in the following patches.
> BPF memory allocator maintains multiple per-cpu area caches for multiple
> area sizes and it needs the size of dynamic per-cpu area to select the
> corresponding cache when bpf program frees the dynamic per-cpu area.
>
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
> ---
> include/linux/percpu.h | 1 +
> mm/percpu.c | 29 +++++++++++++++++++++++++++++
> 2 files changed, 30 insertions(+)
>
> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> index 68fac2e7cbe6..d140d9d79567 100644
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
> @@ -132,6 +132,7 @@ extern void __init setup_per_cpu_areas(void);
> extern void __percpu *__alloc_percpu_gfp(size_t size, size_t align, gfp_t gfp) __alloc_size(1);
> extern void __percpu *__alloc_percpu(size_t size, size_t align) __alloc_size(1);
> extern void free_percpu(void __percpu *__pdata);
> +extern size_t alloc_size_percpu(void __percpu *__pdata);
>
> DEFINE_FREE(free_percpu, void __percpu *, free_percpu(_T))
>
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 7b40b3963f10..f541cfc3cb2d 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2244,6 +2244,35 @@ static void pcpu_balance_workfn(struct work_struct *work)
> mutex_unlock(&pcpu_alloc_mutex);
> }
>
> +/**
> + * alloc_size_percpu - the size of the dynamic percpu area
Can we name this pcpu_alloc_size(). A few other functions are
exposed under pcpu_* so it's a bit easier to keep track of.
> + * @ptr: pointer to the dynamic percpu area
> + *
> + * Return the size of the dynamic percpu area @ptr.
> + *
> + * RETURNS:
> + * The size of the dynamic percpu area.
> + *
> + * CONTEXT:
> + * Can be called from atomic context.
> + */
> +size_t alloc_size_percpu(void __percpu *ptr)
> +{
> + struct pcpu_chunk *chunk;
> + int bit_off, end;
> + void *addr;
> +
> + if (!ptr)
> + return 0;
> +
> + addr = __pcpu_ptr_to_addr(ptr);
> + /* No pcpu_lock here: ptr has not been freed, so chunk is still alive */
Now that percpu variables are floating around more commonly, I think we
or I need to add more validation guards so it's easier to
debug bogus/stale pointers. Potentially like a static_key or Kconfig so
that we take the lock and `test_bit()`.
> + chunk = pcpu_chunk_addr_search(addr);
> + bit_off = (addr - chunk->base_addr) / PCPU_MIN_ALLOC_SIZE;
> + end = find_next_bit(chunk->bound_map, pcpu_chunk_map_bits(chunk), bit_off + 1);
Nit: can you please reflow `bit_off + 1` to the next line. I know we
dropped the line requirement, but percpu.c almost completely still
follows it.
> + return (end - bit_off) * PCPU_MIN_ALLOC_SIZE;
> +}
> +
> /**
> * free_percpu - free percpu area
> * @ptr: pointer to area to free
> --
> 2.29.2
>
Thanks,
Dennis
