Ocfs2 devel - Feb 2020 - [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

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 at linux.alibaba.com>
Sent: Monday, February 3, 2020 1:15 PM
To: Gang He; mark at fasheh.com; jlbec at evilplan.org; gechangwei at live.cn;
Shuning Zhang
Cc: linux-kernel at vger.kernel.org; ocfs2-devel at oss.oracle.com; akpm at
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