linux-kernel - Re: [PATCH 4.4 13/16] ocfs2: should wait dio before inode lock in ocfs2

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Date:   Wed, 6 Dec 2017 09:02:42 +0800
From:   alex chen <alex.chen@...wei.com>
To:     Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     piaojun <piaojun@...wei.com>, Joseph Qi <jiangqi903@...il.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Changwei Ge <ge.changwei@....com>,
        Mark Fasheh <mfasheh@...sity.com>,
        Joel Becker <jlbec@...lplan.org>,
        Junxiao Bi <junxiao.bi@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4.4 13/16] ocfs2: should wait dio before inode lock in
 ocfs2_setattr()

Hi Ben,

Thanks for your reply.

On 2017/12/5 23:49, Ben Hutchings wrote:
> On Wed, 2017-11-22 at 11:12 +0100, Greg Kroah-Hartman wrote:
>> 4.4-stable review patch.  If anyone has any objections, please let me know.
>>
>> ------------------
>>
>> From: alex chen <alex.chen@...wei.com>
>>
>> commit 28f5a8a7c033cbf3e32277f4cc9c6afd74f05300 upstream.
>>
>> we should wait dio requests to finish before inode lock in
>> ocfs2_setattr(), otherwise the following deadlock will happen:
> [...]
> 
> I looked at the kernel-doc for inode_dio_wait():
> 
> /**
>  * inode_dio_wait - wait for outstanding DIO requests to finish
>  * @inode: inode to wait for
>  *
>  * Waits for all pending direct I/O requests to finish so that we can
>  * proceed with a truncate or equivalent operation.
>  *
>  * Must be called under a lock that serializes taking new references
>  * to i_dio_count, usually by inode->i_mutex.
>  */
> 
> Now that ocfs2_setattr() calls this outside of the inode locked region,
> what prevents another task adding a new dio request immediately
> afterward?
>

In the kernel 4.6, firstly, we use the inode_lock() in do_truncate() to
prevent another bio to be issued from this node.
Furthermore, we use the ocfs2_rw_lock() and ocfs2_inode_lock() in ocfs2_setattr()
to guarantee no more bio will be issued from the other nodes in this cluster.

> Also, ocfs2_dio_end_io_write() was introduced in 4.6 and it looks like
> the dio completion path didn't previously take the inode lock.  So it
> doesn't look this fix is needed in 3.18 or 4.4.

Yes, ocfs2_dio_end_io_write() was introduced in 4.6 and the problem this patch
fixes is only exist in the kernel 4.6 and above 4.6.

I'm sorry that I don't clearly point out which the stable version of kernel this patch
will fixes.

Thanks,
Alex

> 
> Ben.
>