netdev - Re: [linux-next:master] BUILD REGRESSION 8cb8311e95e3bb58bd84d6350365f14a718faa6d

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Date:   Thu, 26 May 2022 15:28:25 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Clarke <jrtc27@...c27.com>,
        kernel test robot <lkp@...el.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-riscv@...ts.infradead.org,
        linux-rdma@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-parport@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-mm@...ck.org, linux-fbdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, bpf@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, alsa-devel@...a-project.org
Subject: Re: [linux-next:master] BUILD REGRESSION
 8cb8311e95e3bb58bd84d6350365f14a718faa6d

On Thu, May 26, 2022 at 11:48:32AM +0300, Dan Carpenter wrote:
> On Thu, May 26, 2022 at 02:16:34AM +0100, Matthew Wilcox wrote:
> > Bizarre this started showing up now.  The recent patch was:
> > 
> > -       info->alloced += compound_nr(page);
> > -       inode->i_blocks += BLOCKS_PER_PAGE << compound_order(page);
> > +       info->alloced += folio_nr_pages(folio);
> > +       inode->i_blocks += BLOCKS_PER_PAGE << folio_order(folio);
> > 
> > so it could tell that compound_order() was small, but folio_order()
> > might be large?
> 
> The old code also generates a warning on my test system.  Smatch thinks
> both compound_order() and folio_order() are 0-255.  I guess because of
> the "unsigned char compound_order;" in the struct page.

It'd be nice if we could annotate that as "contains a value between
1 and BITS_PER_LONG - PAGE_SHIFT".  Then be able to optionally enable
a checker that ensures that's true on loads/stores.  Maybe we need a
language that isn't C :-P  Ada can do this ... I don't think Rust can.