[RFC][PATCH 0/5] do not dereference NULL pools in pools' destroy() functions

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

Hello,

RFC

Proposed by Andrew Morton: https://lkml.org/lkml/2015/6/8/583

The existing pools' destroy() functions do not allow NULL pool pointers;
instead, every destructor() caller forced to check if pool is not NULL,
which:
 a) requires additional attention from developers/reviewers
 b) may lead to a NULL pointer dereferences if (a) didn't work


First 3 patches tweak
- kmem_cache_destroy()
- mempool_destroy()
- dma_pool_destroy()

to handle NULL pointers.
Basically, this patch set will:

1) Can prevent us from still undiscovered NULL pointer dereferences.
 (like the one that was addressed in https://lkml.org/lkml/2015/6/5/262)

2) Make a cleanup possible. Things like:
 [..]
         if (xhci->segment_pool)
                 dma_pool_destroy(xhci->segment_pool);
 	..
         if (xhci->device_pool)
                 dma_pool_destroy(xhci->device_pool);
 	..
         if (xhci->small_streams_pool)
                 dma_pool_destroy(xhci->small_streams_pool);
 	..
         if (xhci->medium_streams_pool)
                 dma_pool_destroy(xhci->medium_streams_pool);
 [..]
 
 or
 
 [..]
 fail_dma_pool:
         if (IS_QLA82XX(ha) || ql2xenabledif) {
                 dma_pool_destroy(ha->fcp_cmnd_dma_pool);
                 ha->fcp_cmnd_dma_pool = NULL;
         }
 fail_dl_dma_pool:
         if (IS_QLA82XX(ha) || ql2xenabledif) {
                 dma_pool_destroy(ha->dl_dma_pool);
                 ha->dl_dma_pool = NULL;
         }
 fail_s_dma_pool:
         dma_pool_destroy(ha->s_dma_pool);
         ha->s_dma_pool = NULL;
 [..]

 may now be simplified.


0004 and 0005 are not so necessary, simply because there are not
so many users of these two (added for pool's destroy() functions consistency):
-- zpool_destroy_pool()
-- zs_destroy_pool()

So, 0004 and 0005 can be dropped.


- zbud does kfree() in zbud_destroy_pool(), so I didn't touch it.


Sergey Senozhatsky (5):
  mm/slab_common: allow NULL cache pointer in kmem_cache_destroy()
  mm/mempool: allow NULL `pool' pointer in mempool_destroy()
  mm/dmapool: allow NULL `pool' pointer in dma_pool_destroy()
  mm/zpool: allow NULL `zpool' pointer in zpool_destroy_pool()
  mm/zsmalloc: allow NULL `pool' pointer in zs_destroy_pool()

 mm/dmapool.c     | 3 +++
 mm/mempool.c     | 3 +++
 mm/slab_common.c | 3 +++
 mm/zpool.c       | 3 +++
 mm/zsmalloc.c    | 3 +++
 5 files changed, 15 insertions(+)

-- 
2.4.3.368.g7974889

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