kmem slab magazine ageing deadlock

- The previous magazine ageing sceme relied on the on_each_cpu()
  function to call spl_magazine_age() on each cpu.  It turns out
  this could deadlock with do_flush_tlb_all() which also relies
  on the IPI based on_each_cpu().  To avoid this problem a per-
  magazine delayed work item is created and indepentantly
  scheduled to the correct cpu removing the need for on_each_cpu().
- Additionally two unused fields were removed from the type
  spl_kmem_cache_t, they were hold overs from previous cleanup.
    - struct work_struct work
    - struct timer_list timer

include/sys/kmem.h

@@ -250,10 +250,12 @@ typedef void (*spl_kmem_dtor_t)(void *, void *);
 typedef void (*spl_kmem_reclaim_t)(void *);
 
 typedef struct spl_kmem_magazine {
-        uint32_t		skm_magic;	/* Sanity magic */
+	uint32_t		skm_magic;	/* Sanity magic */
 	uint32_t		skm_avail;	/* Available objects */
 	uint32_t		skm_size;	/* Magazine size */
 	uint32_t		skm_refill;	/* Batch refill size */
+	struct spl_kmem_cache	*skm_cache;	/* Owned by cache */
+	struct delayed_work	skm_work;	/* Magazine reclaim work */
 	unsigned long		skm_age;	/* Last cache access */
 	void			*skm_objs[0];	/* Object pointers */
 } spl_kmem_magazine_t;
@@ -296,8 +298,6 @@ typedef struct spl_kmem_cache {
 	uint32_t		skc_reap;	/* Slab reclaim count */
 	atomic_t		skc_ref;	/* Ref count callers */
 	struct delayed_work	skc_work;	/* Slab reclaim work */
-        struct work_struct work;
-        struct timer_list timer;
 	struct list_head	skc_list;	/* List of caches linkage */
 	struct list_head	skc_complete_list;/* Completely alloc'ed */
 	struct list_head	skc_partial_list; /* Partially alloc'ed */