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Subject: Re: [PATCH v2] mm, slub: emit the "free" trace report before freeing
 memory in kmem_cache_free()
To:     John Hubbard <jhubbard@nvidia.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>
References: <a6824ebe-a0ad-fedb-ada3-c362f9c8f363@huawei.com>
 <6ba0f3d0-cf93-9fb3-d691-962e1cb65eb4@nvidia.com>
From:   Yunfeng Ye <yeyunfeng@huawei.com>
Message-ID: <a0217bfe-87da-8f2a-6a40-edd061baad26@huawei.com>
Date:   Wed, 3 Nov 2021 11:41:26 +0800
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On 2021/11/3 2:37, John Hubbard wrote:
> 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>
> 
Ok, I will fix the typo in the v3 patch.

Thanks.

> 
> thanks,