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SubjectRe: [PATCH v2] mm, slub: emit the "free" trace report before freeing memory in kmem_cache_free()
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On 2021/11/2 19:43, Yunfeng Ye wrote:
> After the memory is freed, it can be immediately allocated by other
> CPUs, before the "free" trace report has been emitted. This causes
> inaccurate traces.
>
> For example, if the following sequence of events occurs:
>
> CPU 0 CPU 1
>
> (1) alloc xxxxxx
> (2) free xxxxxx
> (3) alloc xxxxxx
> (4) free xxxxxx
>
> Then they will be inaccurately reported via tracing, so that they appear
> to have happened in this order:
>
> CPU 0 CPU 1
>
> (1) alloc xxxxxx
> (2) alloc xxxxxx
> (3) free xxxxxx
> (4) free xxxxxx
>
> This makes it look like CPU 1 somehow managed to allocate mmemory that
> CPU 0 still had allocated for itself.
>
> In order to avoid this, emit the "free xxxxxx" tracing report just
> before the actual call to free the memory, instead of just after it.
>
> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> v1 -> v2:
> - Modify the description
> - Add "Reviewed-by"
>
> mm/slub.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 432145d7b4ec..427e62034c3f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3526,8 +3526,8 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
> s = cache_from_obj(s, x);
> if (!s)
> return;
> - slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_);
> trace_kmem_cache_free(_RET_IP_, x, s->name);
> + slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_);
> }

It seems that kmem_cache_free() in mm/slab.c has the same problem.
We can fix it. Thanks.

> EXPORT_SYMBOL(kmem_cache_free);
>

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