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Message-ID: <e9076da5-bd96-1a21-e4af-36eb46409178@linux.alibaba.com>
Date:   Thu, 15 Sep 2022 09:36:59 +0800
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Subject: Re: [PATCH] mm,hwpoison: check mm when killing accessing process
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To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     naoya.horiguchi@nec.com, linmiaohe@huawei.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, cuibixuan@linux.alibaba.com,
        baolin.wang@linux.alibaba.com, zhuo.song@linux.alibaba.com,
        Huang Ying <ying.huang@intel.com>
References: <20220914064935.7851-1-xueshuai@linux.alibaba.com>
 <20220914153542.285f870f728c6129a479a69d@linux-foundation.org>
From:   Shuai Xue <xueshuai@linux.alibaba.com>
In-Reply-To: <20220914153542.285f870f728c6129a479a69d@linux-foundation.org>
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在 2022/9/15 AM6:35, Andrew Morton 写道:
> On Wed, 14 Sep 2022 14:49:35 +0800 Shuai Xue <xueshuai@linux.alibaba.com> wrote:
> 
>> The GHES code calls memory_failure_queue() from IRQ context to queue work
>> into workqueue and schedule it on the current CPU. Then the work is
>> processed in memory_failure_work_func() by kworker and calls
>> memory_failure().
>>
>> When a page is already poisoned, commit a3f5d80ea401 ("mm,hwpoison: send
>> SIGBUS with error virutal address") make memory_failure() call
>> kill_accessing_process() that:
>>
>>     - holds mmap locking of current->mm
>>     - does pagetable walk to find the error virtual address
>>     - and sends SIGBUS to the current process with error info.
>>
>> However, the mm of kworker is not valid. Therefore, check mm when killing
>> accessing process.
> 
> Thanks.
> 
> When fixing a bug, please always describe the user-visible effects of
> tha bug.  I'm thinking "null pointer deref crashes the kernel".

Got it. Thank you :)

> 
>> Fixes: a3f5d80ea401 ("mm,hwpoison: send SIGBUS with error virutal address")
>> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
> 
> I'll add cc:stable.

Thanks.

> 
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -743,6 +743,9 @@ static int kill_accessing_process(struct task_struct *p, unsigned long pfn,
>>  	};
>>  	priv.tk.tsk = p;
>>  
>> +	if (!p->mm)
>> +		return -EFAULT;
>> +
>>  	mmap_read_lock(p->mm);
>>  	ret = walk_page_range(p->mm, 0, TASK_SIZE, &hwp_walk_ops,
>>  			      (void *)&priv);
>> @@ -751,6 +754,7 @@ static int kill_accessing_process(struct task_struct *p, unsigned long pfn,
>>  	else
>>  		ret = 0;
>>  	mmap_read_unlock(p->mm);
>> +
>>  	return ret > 0 ? -EHWPOISON : -EFAULT;
>>  }
> 
> This is an unrelated change which doesn't appear to match the style in
> memory-failure.c, so I'll drop this hunk.

I see, thanks.

Cheers,
Shuai