Date:   Fri, 3 Feb 2023 17:31:07 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     David Howells <dhowells@redhat.com>
Cc:     Christoph Hellwig <hch@lst.de>, John Hubbard <jhubbard@nvidia.com>,
        David Hildenbrand <david@redhat.com>,
        syzbot <syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com>,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: How does ftruncate() interact with DIO read?
Message-ID: <20230203163107.GA4082@lst.de>
References: <2112099.1675441439@warthog.procyon.org.uk> <2076817.1675434996@warthog.procyon.org.uk> <72029a93-1150-1994-916f-b15ef0befd49@nvidia.com> <e8065d6a-d2f9-60aa-8541-8dfc8e9b608f@redhat.com> <000000000000b0b3c005f3a09383@google.com> <822863.1675327935@warthog.procyon.org.uk> <1265629.1675350909@warthog.procyon.org.uk> <2116614.1675441630@warthog.procyon.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <2116614.1675441630@warthog.procyon.org.uk>
User-Agent: Mutt/1.5.17 (2007-11-01)
Precedence: bulk

On Fri, Feb 03, 2023 at 04:27:10PM +0000, David Howells wrote:
> Hi Christoph,
> 
> What does ftruncate() do if there's a conflicting DIO read happening on the
> same file?  Does it cancel the bio?

There is no way to cancel a bio.  ->setattr is supposed to call
inode_dio_wait to wait for pending I/O, although some file systems
like btrfs have their own hand crafted and more complicated version
of that.