Re: [PATCH] ocfs2: fix the oops problem when write cloned file

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>
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>
Subject: Re: [PATCH] ocfs2: fix the oops problem when write cloned file
Date: Mon, 3 Feb 2020 05:32:28 +0000	[thread overview]
Message-ID: <CH2PR18MB3206844EE94EC90A2CBFF85CCF000@CH2PR18MB3206.namprd18.prod.outlook.com> (raw)
In-Reply-To: <de23176f-5b84-a785-80a2-0bdc8e3a0fab@linux.alibaba.com>

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