linux-kernel - Re: [Cluster-devel] [PATCH 05/12] gfs2: fix O

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Message-ID: <CAHc6FU45m59PjBWWO=F740_jyOtKSwc__XfYhP84WkpK0uqcWQ@mail.gmail.com>
Date:   Thu, 6 Feb 2020 16:31:58 +0100
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-xfs@...r.kernel.org,
        linux-fsdevel <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 <linux-ext4@...r.kernel.org>,
        cluster-devel <cluster-devel@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Cluster-devel] [PATCH 05/12] gfs2: fix O_SYNC write handling

Hi Christoph,

thanks for this patch, and sorry for taking so long to react.

On Tue, Jan 14, 2020 at 5:54 PM Christoph Hellwig <hch@....de> wrote:
> Don't ignore the return value from generic_write_sync for the direct to
> buffered I/O callback case when written is non-zero.  Also don't bother
> to call generic_write_sync for the pure direct I/O case, as iomap_dio_rw
> already takes care of that.

I like the idea, but the patch as is doesn't quite work: iomap_dio_rw
already bumps iocb->ki_pos, so we end up with the wrong value by
adding the (direct + buffered) write size again.
We'd probably also be better served by replacing
filemap_write_and_wait_range with generic_write_sync + IOCB_DSYNC in
the buffered fallback case. I'll send an update that you'll hopefully
like.

Andreas