Re: [PATCH v2 3/7] buffer: Fix grow_buffers() for block size > PAGE_SIZE

[Naresh Kamboju <naresh.kamboju@linaro.org>]

Hi Nathan,

On Mon, 13 Nov 2023 at 22:50, Nathan Chancellor <nathan@kernel.org> wrote:
>
> On Mon, Nov 13, 2023 at 09:10:06AM -0800, Andrew Morton wrote:
> > On Sun, 12 Nov 2023 12:52:00 +0800 kernel test robot <lkp@intel.com> wrote:
> >
> > > Hi Matthew,
> > >
> > > kernel test robot noticed the following build errors:
> > >
> > > [auto build test ERROR on akpm-mm/mm-everything]
> > > [also build test ERROR on linus/master next-20231110]
> > > [cannot apply to v6.6]
> > > [If your patch is applied to the wrong git tree, kindly drop us a note.
> > > And when submitting patch, we suggest to use '--base' as documented in
> > > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> > >
> > > url:    https://github.com/intel-lab-lkp/linux/commits/Matthew-Wilcox-Oracle/buffer-Return-bool-from-grow_dev_folio/20231110-051651
> > > base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> > > patch link:    https://lore.kernel.org/r/20231109210608.2252323-4-willy%40infradead.org
> > > patch subject: [PATCH v2 3/7] buffer: Fix grow_buffers() for block size > PAGE_SIZE
> > > config: hexagon-comet_defconfig (https://download.01.org/0day-ci/archive/20231112/202311121240.AN8GbAbe-lkp@intel.com/config)
> > > compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231112/202311121240.AN8GbAbe-lkp@intel.com/reproduce)
> > >
> > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > the same patch/commit), kindly add following tags
> > > | Reported-by: kernel test robot <lkp@intel.com>
> > > | Closes: https://lore.kernel.org/oe-kbuild-all/202311121240.AN8GbAbe-lkp@intel.com/

KFT CI also have been noticing this build problem on Linux next.
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>

> > >
> > > All errors (new ones prefixed by >>):
> > >
> > > >> ld.lld: error: undefined symbol: __muloti4
> > >    >>> referenced by buffer.c
> > >    >>>               fs/buffer.o:(bdev_getblk) in archive vmlinux.a
> > >    >>> referenced by buffer.c
> > >    >>>               fs/buffer.o:(bdev_getblk) in archive vmlinux.a
> > >
> >
> > What a peculiar compiler.
> >
> > I assume this fixes?
> >
> > --- a/fs/buffer.c~buffer-fix-grow_buffers-for-block-size-page_size-fix
> > +++ a/fs/buffer.c
> > @@ -1099,7 +1099,7 @@ static bool grow_buffers(struct block_de
> >       }
> >
> >       /* Create a folio with the proper size buffers */
> > -     return grow_dev_folio(bdev, block, pos / PAGE_SIZE, size, gfp);
> > +     return grow_dev_folio(bdev, block, pos >> PAGE_SHIFT, size, gfp);
> >  }
> >
> >  static struct buffer_head *
> > _
> >
> >
>
> No, this is not a division libcall. This seems to be related to the
> types of the variables used in __builtin_mul_overflow() :/ for some odd
> reason, clang generates a libcall when passing in an 'unsigned long
> long' and 'unsigned int', which apparently has not been done before in
> the kernel?
>
> https://github.com/ClangBuiltLinux/linux/issues/1958
> https://godbolt.org/z/csfGc6z6c
>
> A cast would work around this but that could have other implications I
> am not aware of (I've done little further investigation due to LPC):

Thanks for providing this fix patch.


> diff --git a/fs/buffer.c b/fs/buffer.c
> index 4eb44ccdc6be..d39934783743 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1091,7 +1091,7 @@ static bool grow_buffers(struct block_device *bdev, sector_t block,
>          * Check for a block which lies outside our maximum possible
>          * pagecache index.
>          */
> -       if (check_mul_overflow(block, size, &pos) || pos > MAX_LFS_FILESIZE) {
> +       if (check_mul_overflow(block, (u64)size, &pos) || pos > MAX_LFS_FILESIZE) {
>                 printk(KERN_ERR "%s: requested out-of-range block %llu for device %pg\n",
>                         __func__, (unsigned long long)block,
>                         bdev);
>
> Cheers,
> Nathan

- Naresh