From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by smtp.lore.kernel.org (Postfix) with ESMTP id 64AE4C43334
	for <linux-fsdevel@archiver.kernel.org>; Tue,  7 Jun 2022 16:06:57 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S236694AbiFGQG4 (ORCPT
        <rfc822;linux-fsdevel@archiver.kernel.org>);
        Tue, 7 Jun 2022 12:06:56 -0400
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39570 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S235088AbiFGQGz (ORCPT
        <rfc822;linux-fsdevel@vger.kernel.org>);
        Tue, 7 Jun 2022 12:06:55 -0400
Received: from zeniv-ca.linux.org.uk (zeniv-ca.linux.org.uk [IPv6:2607:5300:60:148a::1])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5A8CBFF5AC
        for <linux-fsdevel@vger.kernel.org>; Tue,  7 Jun 2022 09:06:54 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
        d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type:
        MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To:
        Content-Transfer-Encoding:Content-ID:Content-Description;
        bh=jx0PIwsySTFEp9nSZzszFo1rfglY5ANWvXLXoBrw8Kk=; b=ZDJaIpbCeJ09ORwN0+0lmuyM6u
        vsnhZ/zXnCz21kG3xLfuz6UeB5W2Xxf9AOPTgxudpgKJOfiQnbXgSTdgL9lavAgm4MRIQGfMy/8uX
        z/Z0cJgj/mZFKdXQkP3A1fyB4sSk8zbBKbwclTs8lWN/IH0LddpjYNlGSleyjIU2zM7pr/TwDOWSE
        Iu2FLQDA2BSJdokPuI7CPGnQY6GswqYAmA+IL6W126HDbTdtixjEZKWxQanbYWScgrNFJpTT+LS8h
        q7QOthycjORlASumyzlsy0eKYITnEoZL6+gt0q9NVdLiUcoHQXra3hlIY/odeyTNZeKJ6qQ1GrwFp
        cKcgVreQ==;
Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux))
        id 1nybjJ-004mxZ-6z; Tue, 07 Jun 2022 16:06:53 +0000
Date:   Tue, 7 Jun 2022 16:06:53 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christoph Hellwig <hch@lst.de>
Cc:     linux-fsdevel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH 2/9] btrfs_direct_write(): cleaner way to handle
 generic_write_sync() suppression
Message-ID: <Yp93nbSBggvxjVqa@zeniv-ca.linux.org.uk>
References: <Yp7PTZ2nckKDTkKu@zeniv-ca.linux.org.uk>
 <Yp7PlaCTJF19m2sG@zeniv-ca.linux.org.uk>
 <20220607044217.GB7887@lst.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220607044217.GB7887@lst.de>
Sender: Al Viro <viro@ftp.linux.org.uk>
Precedence: bulk
List-ID: <linux-fsdevel.vger.kernel.org>
X-Mailing-List: linux-fsdevel@vger.kernel.org

On Tue, Jun 07, 2022 at 06:42:17AM +0200, Christoph Hellwig wrote:

> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index 370c3241618a..0f16479b13d6 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -548,7 +548,7 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> >  		}
> >  
> >  		/* for data sync or sync, we need sync completion processing */
> > -		if (iocb->ki_flags & IOCB_DSYNC)
> > +		if (iocb->ki_flags & IOCB_DSYNC && !(dio_flags & IOMAP_DIO_NOSYNC))
> 
> Same here.

Dealt with in the next commit, actually.

> Also the FUA check below needs to check IOMAP_DIO_NOSYNC as
> well.

Does it?  AFAICS, we don't really care about REQ_FUA on any requests - what
btrfs hack tries to avoid is stepping into
        if (ret > 0 && (dio->flags & IOMAP_DIO_NEED_SYNC))
		ret = generic_write_sync(iocb, ret);
with generic_write_sync() called by btrfs_do_write_iter() after it has
dropped the lock held through btrfs_direct_write().  Do we want to
suppress REQ_FUA on the requests generated by __iomap_dio_rw() in
that case (DSYNC, !SYNC)?  Confused...