Re: [Qemu-devel] [PATCH v19 1/7] xbitmap: Introduce xbitmap

[kbuild test robot]

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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