From: John Hubbard <jhubbard@nvidia.com>
To: Yunfeng Ye <yeyunfeng@huawei.com>,
cl@linux.com, penberg@kernel.org, rientjes@google.com,
iamjoonsoo.kim@lge.com, Andrew Morton <akpm@linux-foundation.org>,
vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: songmuchun@bytedance.com, willy@infradead.org,
wuxu.wu@huawei.com, Hewenliang <hewenliang4@huawei.com>
Subject: Re: [PATCH v2] mm, slub: emit the "free" trace report before freeing memory in kmem_cache_free()
Date: Tue, 2 Nov 2021 11:37:11 -0700 [thread overview]
Message-ID: <6ba0f3d0-cf93-9fb3-d691-962e1cb65eb4@nvidia.com> (raw)
In-Reply-To: <a6824ebe-a0ad-fedb-ada3-c362f9c8f363@huawei.com>
On 11/2/21 04:43, 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
I see I created a typo for you, sorry about that: s/mmemory/memory/
But anyway, the wording looks good now. Please feel free to add:
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks,
--
John Hubbard
NVIDIA
> 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_);
> }
> EXPORT_SYMBOL(kmem_cache_free);
>
next prev parent reply other threads:[~2021-11-02 18:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-02 11:43 [PATCH v2] mm, slub: emit the "free" trace report before freeing memory in kmem_cache_free() Yunfeng Ye
2021-11-02 13:53 ` Tang Yizhou
2021-11-02 14:39 ` Vlastimil Babka
2021-11-03 3:39 ` Yunfeng Ye
2021-11-02 18:37 ` John Hubbard [this message]
2021-11-03 3:41 ` Yunfeng Ye
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