linux-kernel - Re: [PATCH v2 16/16] iomap: Make readpage synchronous

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Message-ID: <20201015190312.GB20115@casper.infradead.org>
Date:   Thu, 15 Oct 2020 20:03:12 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-afs@...ts.infradead.org, ceph-devel@...r.kernel.org,
        linux-cifs@...r.kernel.org, ecryptfs@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-mtd@...ts.infradead.org,
        Richard Weinberger <richard@....at>, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v2 16/16] iomap: Make readpage synchronous

On Thu, Oct 15, 2020 at 06:58:48PM +0100, Christoph Hellwig wrote:
> On Thu, Oct 15, 2020 at 05:43:33PM +0100, Matthew Wilcox wrote:
> > I prefer assigning ctx conditionally to propagating the knowledge
> > that !rac means synchronous.  I've gone with this:
> 
> And I really hate these kinds of conditional assignments.  If the
> ->rac check is too raw please just add an explicit
> 
> 	bool synchronous : 1;
> 
> flag.

I honestly don't see the problem.  We have to assign the status
conditionally anyway so we don't overwrite an error with a subsequent
success.

> True.  I'd still prefer the AOP_UPDATED_PAGE as the fallthrough case
> and an explicit goto out_unlock, though.

So this?

        if (ctx.bio) {
                submit_bio(ctx.bio);
                wait_for_completion(&ctx.done);
                if (ret < 0)
                        goto err;
                ret = blk_status_to_errno(ctx.status);
        }

        if (ret < 0)
                goto err;
        return AOP_UPDATED_PAGE;
err:
        unlock_page(page);
        return ret;