linux-kernel - Re: [PATCH v19 1/7] xbitmap: Introduce xbitmap

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Date:   Fri, 15 Dec 2017 19:05:07 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     kbuild-all@...org, virtio-dev@...ts.oasis-open.org,
        linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mst@...hat.com, mhocko@...nel.org,
        akpm@...ux-foundation.org, mawilcox@...rosoft.com,
        david@...hat.com, penguin-kernel@...ove.SAKURA.ne.jp,
        cornelia.huck@...ibm.com, mgorman@...hsingularity.net,
        aarcange@...hat.com, amit.shah@...hat.com, pbonzini@...hat.com,
        willy@...radead.org, wei.w.wang@...el.com,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu@...yun.com, nilal@...hat.com, riel@...hat.com
Subject: Re: [PATCH v19 1/7] xbitmap: Introduce xbitmap

Hi Matthew,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.15-rc3]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Wei-Wang/Virtio-balloon-Enhancement/20171215-100525
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)


vim +29 lib/xbitmap.c

     5	
     6	/**
     7	 *  xb_set_bit - set a bit in the xbitmap
     8	 *  @xb: the xbitmap tree used to record the bit
     9	 *  @bit: index of the bit to set
    10	 *
    11	 * This function is used to set a bit in the xbitmap. If the bitmap that @bit
    12	 * resides in is not there, the per-cpu ida_bitmap will be taken.
    13	 *
    14	 * Returns: 0 on success. %-EAGAIN indicates that @bit was not set.
    15	 */
    16	int xb_set_bit(struct xb *xb, unsigned long bit)
    17	{
    18		int err;
    19		unsigned long index = bit / IDA_BITMAP_BITS;
    20		struct radix_tree_root *root = &xb->xbrt;
    21		struct radix_tree_node *node;
    22		void **slot;
    23		struct ida_bitmap *bitmap;
    24		unsigned long ebit;
    25	
    26		bit %= IDA_BITMAP_BITS;
    27		ebit = bit + 2;
    28	
  > 29		err = __radix_tree_create(root, index, 0, &node, &slot);
    30		if (err)
    31			return err;
    32		bitmap = rcu_dereference_raw(*slot);
    33		if (radix_tree_exception(bitmap)) {
    34			unsigned long tmp = (unsigned long)bitmap;
    35	
    36			if (ebit < BITS_PER_LONG) {
    37				tmp |= 1UL << ebit;
    38				rcu_assign_pointer(*slot, (void *)tmp);
    39				return 0;
    40			}
    41			bitmap = this_cpu_xchg(ida_bitmap, NULL);
    42			if (!bitmap)
    43				return -EAGAIN;
    44			memset(bitmap, 0, sizeof(*bitmap));
    45			bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
    46			rcu_assign_pointer(*slot, bitmap);
    47		}
    48	
    49		if (!bitmap) {
    50			if (ebit < BITS_PER_LONG) {
    51				bitmap = (void *)((1UL << ebit) |
    52						RADIX_TREE_EXCEPTIONAL_ENTRY);
  > 53				__radix_tree_replace(root, node, slot, bitmap, NULL);
    54				return 0;
    55			}
    56			bitmap = this_cpu_xchg(ida_bitmap, NULL);
    57			if (!bitmap)
    58				return -EAGAIN;
    59			memset(bitmap, 0, sizeof(*bitmap));
    60			__radix_tree_replace(root, node, slot, bitmap, NULL);
    61		}
    62	
    63		__set_bit(bit, bitmap->bitmap);
    64		return 0;
    65	}
    66	EXPORT_SYMBOL(xb_set_bit);
    67	

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