linux-kernel - Re: [PATCH 08/12] ext4: hold i

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Date:   Wed, 15 Jan 2020 07:48:27 +0100
From:   Christoph Hellwig <hch@....de>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Christoph Hellwig <hch@....de>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Waiman Long <longman@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-ext4@...r.kernel.org, cluster-devel@...hat.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 08/12] ext4: hold i_rwsem until AIO completes

On Tue, Jan 14, 2020 at 04:50:23PM -0500, Theodore Y. Ts'o wrote:
> I note that you've dropped the inode_dio_wait() in ext4's ZERO_RANGE,
> COLLAPSE_RANGE, INSERT_RANGE, etc.  We had added these to avoid
> problems when various fallocate operations which modify the inode's
> logical->physical block mapping racing with direct I/O (both reads or
> writes).
> 
> I don't see a replacement protection in this patch series.  How does
> are file systems supported to protect against such races?

By holding i_rwsem until the direct I/O operations are finished, and
not just until they are sumbitted.