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

From: Christoph Hellwig <hch@lst.de>
To: kernel test robot <lkp@intel.com>
Cc: Christoph Hellwig <hch@lst.de>,
	oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org,
	Carlos Maiolino <cem@kernel.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	linux-riscv@lists.infradead.org
Subject: Re: fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '_x' is never less than zero.
Date: Mon, 17 Feb 2025 10:24:45 +0100	[thread overview]
Message-ID: <20250217092445.GA29568@lst.de> (raw)
In-Reply-To: <202502171326.j4Xd3I0j-lkp@intel.com>

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?

> 
> 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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