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From:   Gang He <GHe@suse.com>
To:     Joseph Qi <joseph.qi@linux.alibaba.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>
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        "ocfs2-devel@oss.oracle.com" <ocfs2-devel@oss.oracle.com>,
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Subject: Re: [PATCH] ocfs2: fix the oops problem when write cloned file
Thread-Topic: [PATCH] ocfs2: fix the oops problem when write cloned file
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Date:   Mon, 3 Feb 2020 05:32:28 +0000
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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.

Thanks
Gang

________________________________________
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