[linux-next:master] BUILD REGRESSION 8cb8311e95e3bb58bd84d6350365f14a718faa6d

[Matthew Wilcox]

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.