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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20201015164333.GA20115@casper.infradead.org>
Date:   Thu, 15 Oct 2020 17:43:33 +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 10:42:03AM +0100, Christoph Hellwig wrote:
> > +static void iomap_read_page_end_io(struct bio_vec *bvec,
> > +		struct completion *done, bool error)
> 
> I really don't like the parameters here.  Part of the problem is
> that ctx is only assigned to bi_private conditionally, which can
> easily be fixed.  The other part is the strange bool error when
> we can just pass on bi_stats.  See the patch at the end of what
> I'd do intead.

I prefer assigning ctx conditionally to propagating the knowledge
that !rac means synchronous.  I've gone with this:

 static void iomap_read_page_end_io(struct bio_vec *bvec,
-               struct completion *done, bool error)
+               struct iomap_readpage_ctx *ctx, blk_status_t status)
 {
        struct page *page = bvec->bv_page;
        struct iomap_page *iop = to_iomap_page(page);
 
-       if (!error)
+       if (status == BLK_STS_OK) {
                iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);
+       } else if (ctx && ctx->status == BLK_STS_OK) {
+               ctx->status = status;
+       }
 
        if (!iop ||
            atomic_sub_and_test(bvec->bv_len, &iop->read_bytes_pending)) {
-               if (done)
-                       complete(done);
+               if (ctx)
+                       complete(&ctx->done);
                else
                        unlock_page(page);
        }

> >  	} else {
> >  		WARN_ON_ONCE(ctx.cur_page_in_bio);
> > -		unlock_page(page);
> > +		complete(&ctx.done);
> >  	}
> >  
> > +	wait_for_completion(&ctx.done);
> 
> I don't think we need the complete / wait_for_completion dance in
> this case.
> 
> > +	if (ret >= 0)
> > +		ret = blk_status_to_errno(ctx.status);
> > +	if (ret == 0)
> > +		return AOP_UPDATED_PAGE;
> > +	unlock_page(page);
> > +	return ret;
> 
> Nipick, but I'd rather have a goto out_unlock for both error case
> and have the AOP_UPDATED_PAGE for the normal path straight in line.
> 
> Here is an untested patch with my suggestions:

I think we can go a little further here:

@@ -340,16 +335,12 @@ iomap_readpage(struct page *page, const struct iomap_ops *
ops)
 
        if (ctx.bio) {
                submit_bio(ctx.bio);
-               WARN_ON_ONCE(!ctx.cur_page_in_bio);
-       } else {
-               WARN_ON_ONCE(ctx.cur_page_in_bio);
-               complete(&ctx.done);
+               wait_for_completion(&ctx.done);
+               if (ret > 0)
+                       ret = blk_status_to_errno(ctx.status);
        }
 
-       wait_for_completion(&ctx.done);
        if (ret >= 0)
-               ret = blk_status_to_errno(ctx.status);
-       if (ret == 0)
                return AOP_UPDATED_PAGE;
        unlock_page(page);
        return ret;


... there's no need to call blk_status_to_errno if we never submitted a bio.