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Subject: Re: [PATCH] ocfs2: fix the oops problem when write cloned file
To:     Gang He <GHe@suse.com>, "mark@fasheh.com" <mark@fasheh.com>,
        "jlbec@evilplan.org" <jlbec@evilplan.org>,
        "gechangwei@live.cn" <gechangwei@live.cn>,
        Shuning Zhang <sunny.s.zhang@oracle.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "ocfs2-devel@oss.oracle.com" <ocfs2-devel@oss.oracle.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>
References: <20200121050153.13290-1-ghe@suse.com>
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From:   Joseph Qi <joseph.qi@linux.alibaba.com>
Message-ID: <9dfcde60-f8da-6458-4992-ae1d5dcc1ec1@linux.alibaba.com>
Date:   Mon, 3 Feb 2020 16:15:12 +0800
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On 20/2/3 13:32, Gang He wrote:
> Hi Joseph,
> 
> before calling ocfs2_refcount_cow() in the function ocfs2_prepare_inode_for_write(), we do not use inode buffer_head.
> So, we can let buffer_head is NULL.
> But, when we invoke ocfs2_refcount_cow() function, we have to pass inode buffer_head without NULL pointer.
> That is why writing clone file will cause oops and kill the user-space process.
> 
Okay, so before commit e74540b28556, we will always get a valid buffer
head in ocfs2_prepare_inode_for_refcount().
You can feel free to add:
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>

BTW, you'd better resend the patch in a single thread, for the
convenience of merging by akpm.

> 
> ________________________________________
> From: Joseph Qi <joseph.qi@linux.alibaba.com>
> Sent: Monday, February 3, 2020 1:15 PM
> To: Gang He; mark@fasheh.com; jlbec@evilplan.org; gechangwei@live.cn; Shuning Zhang
> Cc: linux-kernel@vger.kernel.org; ocfs2-devel@oss.oracle.com; akpm@linux-foundation.org
> Subject: Re: [PATCH] ocfs2: fix the oops problem when write cloned file
> 
> 
> 
> On 20/2/3 10:17, Gang He wrote:
>> Hello Joseph, Changwei, Sunny and all,
>>
>> Could you help to review this patch?
>> This patch will fix the oops problem caused by write ocfs2 clone files.
>> The root cause is inode buffer head is NULL when calling ocfs2_refcount_cow.
>> Secondly, we should use EX meta lock when calling ocfs2_refcount_cow.
>>
> Before commit e74540b28556, we may also use NULL buffer head in case of
> overwrite, so why there is no such issue before?
> 
> Thanks,
> Joseph
>