Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RFC] iomap: fix race between readahead and direct write
To:     Matthew Wilcox <willy@infradead.org>
CC:     <hch@infradead.org>, <darrick.wong@oracle.com>,
        <linux-xfs@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <houtao1@huawei.com>,
        <zhengbin13@huawei.com>, <yi.zhang@huawei.com>
References: <20200116063601.39201-1-yukuai3@huawei.com>
 <20200118230826.GA5583@bombadil.infradead.org>
From:   "yukuai (C)" <yukuai3@huawei.com>
Message-ID: <f5328338-1a2d-38b4-283f-3fb97ad37133@huawei.com>
Date:   Sun, 19 Jan 2020 09:34:32 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <20200118230826.GA5583@bombadil.infradead.org>
Content-Type: text/plain; charset="gbk"; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 2020/1/19 7:08, Matthew Wilcox wrote:
> It's worth noting that my patch series from earlier this week to
> redesign the readahead API will fix this problem.  Direct write will block
> on the locked pages in the page cache.

Thank you for your response!

In this case, direct write finish while page do not exist in the page
cache. This is the fundamental condition of the race, because readahead
won't allocate page if page exist in page cache.

By the way, in the current logic, if page exist in page cache, direct
write need to hold lock for page in invalidate_inode_pages2_range().

Thanks!
Yu Kuai