[bug report] mm, slab/slub: introduce kmalloc-reclaimable caches

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Vlastimil Babka,

The patch 1291523f2c1d: "mm, slab/slub: introduce kmalloc-reclaimable
caches" from Oct 26, 2018, leads to the following static checker
warning:

	./include/linux/slab.h:585 kmalloc_node()
	warn: array off by one? 'kmalloc_caches[kmalloc_type(flags)]' '0-3 == 3'

./include/linux/slab.h
   298  /*
   299   * Whenever changing this, take care of that kmalloc_type() and
   300   * create_kmalloc_caches() still work as intended.
   301   */
   302  enum kmalloc_cache_type {
   303          KMALLOC_NORMAL = 0,
   304          KMALLOC_RECLAIM,
   305  #ifdef CONFIG_ZONE_DMA
   306          KMALLOC_DMA,
   307  #endif
   308          NR_KMALLOC_TYPES


The kmalloc_caches[] array has NR_KMALLOC_TYPES elements.

   309  };
   310  
   311  #ifndef CONFIG_SLOB
   312  extern struct kmem_cache *
   313  kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1];
   314  
   315  static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags)
   316  {
   317          int is_dma = 0;
   318          int type_dma = 0;
   319          int is_reclaimable;
   320  
   321  #ifdef CONFIG_ZONE_DMA
   322          is_dma = !!(flags & __GFP_DMA);
   323          type_dma = is_dma * KMALLOC_DMA;
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

KMALLOC_DMA is the last possible valid index.

   324  #endif
   325  
   326          is_reclaimable = !!(flags & __GFP_RECLAIMABLE);
   327  
   328          /*
   329           * If an allocation is both __GFP_DMA and __GFP_RECLAIMABLE, return
   330           * KMALLOC_DMA and effectively ignore __GFP_RECLAIMABLE
   331           */
   332          return type_dma + (is_reclaimable & !is_dma) * KMALLOC_RECLAIM;
                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

We're adding one to it.  This is mm/ so I assume this works, but it's
pretty confusing.

   333  }

regards,
dan carpenter