Re: fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '_x' is never less than zero.

[Alexandre Ghiti]

Hi Christoph,

On 17/02/2025 10:24, Christoph Hellwig wrote:
> On Mon, Feb 17, 2025 at 01:53:08PM +0800, kernel test robot wrote:
> > New smatch warnings:
> > fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '_x' is never less than zero.
> Looks like this is an issue in the riscv virt_to_page implementation
> which also shows up in various other places.  Any chance this could get
> fixed in the riscv code?


To me, the only test that could give rise to this warning is the last 
part of:

#define is_linear_mapping(x) \
        ((x) >= PAGE_OFFSET && (!IS_ENABLED(CONFIG_64BIT) || (x) < 
PAGE_OFFSET + KERN_VIRT_SIZE))

But given that the config is a 32-bit config, it should not be evaluated 
at all.

Could that be a false-positive and then an issue in smatch?

Thanks,

Alex


> > Old smatch warnings:
> > fs/xfs/xfs_linux.h:283 kmem_to_page() warn: unsigned '_x' is never less than zero.
> > fs/xfs/xfs_buf.c:761 xfs_buf_get_map() error: we previously assumed 'bp' could be null (see line 743)
> > arch/riscv/include/asm/atomic.h:218 arch_atomic_fetch_add_unless() warn: inconsistent indenting
> >
> > vim +/_x +1534 fs/xfs/xfs_buf.c
> >
> >    1518	
> >    1519	static void
> >    1520	xfs_buf_submit_bio(
> >    1521		struct xfs_buf		*bp)
> >    1522	{
> >    1523		unsigned int		size = BBTOB(bp->b_length);
> >    1524		unsigned int		map = 0, p;
> >    1525		struct blk_plug		plug;
> >    1526		struct bio		*bio;
> >    1527	
> >    1528		bio = bio_alloc(bp->b_target->bt_bdev, bp->b_page_count,
> >    1529				xfs_buf_bio_op(bp), GFP_NOIO);
> >    1530		bio->bi_private = bp;
> >    1531		bio->bi_end_io = xfs_buf_bio_end_io;
> >    1532	
> >    1533		if (bp->b_flags & _XBF_KMEM) {
> > > 1534			__bio_add_page(bio, virt_to_page(bp->b_addr), size,
> >    1535					bp->b_offset);
> >    1536		} else {
> >    1537			for (p = 0; p < bp->b_page_count; p++)
> >    1538				__bio_add_page(bio, bp->b_pages[p], PAGE_SIZE, 0);
> >    1539			bio->bi_iter.bi_size = size; /* limit to the actual size used */
> >    1540	
> >    1541			if (xfs_buf_is_vmapped(bp))
> >    1542				flush_kernel_vmap_range(bp->b_addr,
> >    1543						xfs_buf_vmap_len(bp));
> >    1544		}
> >    1545	
> >    1546		/*
> >    1547		 * If there is more than one map segment, split out a new bio for each
> >    1548		 * map except of the last one.  The last map is handled by the
> >    1549		 * remainder of the original bio outside the loop.
> >    1550		 */
> >    1551		blk_start_plug(&plug);
> >    1552		for (map = 0; map < bp->b_map_count - 1; map++) {
> >    1553			struct bio	*split;
> >    1554	
> >    1555			split = bio_split(bio, bp->b_maps[map].bm_len, GFP_NOFS,
> >    1556					&fs_bio_set);
> >    1557			split->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
> >    1558			bio_chain(split, bio);
> >    1559			submit_bio(split);
> >    1560		}
> >    1561		bio->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
> >    1562		submit_bio(bio);
> >    1563		blk_finish_plug(&plug);
> >    1564	}
> >    1565	
> >
> > --
> > 0-DAY CI Kernel Test Service
> > https://github.com/intel/lkp-tests/wiki
> ---end quoted text---
>
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