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Michal Hocko 751e5f5c75 vmstat: allocate vmstat_wq before it is used 
kernel test robot has reported the following crash:

  BUG: unable to handle kernel NULL pointer dereference at 00000100
  IP: [<c1074df6>] __queue_work+0x26/0x390
  *pdpt = 0000000000000000 *pde = f000ff53f000ff53 *pde = f000ff53f000ff53
  Oops: 0000 [#1] PREEMPT PREEMPT SMP SMP
  CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.4.0-rc4-00139-g373ccbe #1
  Workqueue: events vmstat_shepherd
  task: cb684600 ti: cb7ba000 task.ti: cb7ba000
  EIP: 0060:[<c1074df6>] EFLAGS: 00010046 CPU: 0
  EIP is at __queue_work+0x26/0x390
  EAX: 00000046 EBX: cbb37800 ECX: cbb37800 EDX: 00000000
  ESI: 00000000 EDI: 00000000 EBP: cb7bbe68 ESP: cb7bbe38
   DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
  CR0: 8005003b CR2: 00000100 CR3: 01fd5000 CR4: 000006b0
  Stack:
  Call Trace:
    __queue_delayed_work+0xa1/0x160
    queue_delayed_work_on+0x36/0x60
    vmstat_shepherd+0xad/0xf0
    process_one_work+0x1aa/0x4c0
    worker_thread+0x41/0x440
    kthread+0xb0/0xd0
    ret_from_kernel_thread+0x21/0x40

The reason is that start_shepherd_timer schedules the shepherd work item
which uses vmstat_wq (vmstat_shepherd) before setup_vmstat allocates
that workqueue so if the further initialization takes more than HZ we
might end up scheduling on a NULL vmstat_wq.  This is really unlikely
but not impossible.

Fixes: 373ccbe592 ("mm, vmstat: allow WQ concurrency to discover memory reclaim doesn't make any progress")
Reported-by: kernel test robot <ying.huang@linux.intel.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Tested-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: stable@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2016-01-08 23:47:54 -08:00
..
kasan kasan: fix kmemleak false-positive in kasan_module_alloc() 2015-11-20 16:17:32 -08:00
Kconfig mm: make compound_head() robust 2015-11-06 17:50:42 -08:00
Kconfig.debug mm/debug_pagealloc: remove obsolete Kconfig options 2015-01-08 15:10:52 -08:00
Makefile media updates for v4.3-rc1 2015-09-11 16:42:39 -07:00
backing-dev.c mm, vmstat: allow WQ concurrency to discover memory reclaim doesn't make any progress 2015-12-12 10:15:34 -08:00
balloon_compaction.c mm: page migration trylock newpage at same level as oldpage 2015-11-05 19:34:48 -08:00
bootmem.c bootmem: avoid freeing to bootmem after bootmem is done 2015-09-08 15:35:28 -07:00
cleancache.c cleancache: remove limit on the number of cleancache enabled filesystems 2015-04-14 16:49:03 -07:00
cma.c mm/cma.c: suppress warning 2015-11-05 19:34:48 -08:00
cma.h mm: cma: mark cma_bitmap_maxno() inline in header 2015-08-14 15:56:32 -07:00
cma_debug.c mm/cma_debug: correct size input to bitmap function 2015-07-17 16:39:54 -07:00
compaction.c mm, compaction: distinguish contended status in tracepoints 2015-11-05 19:34:48 -08:00
debug-pagealloc.c mm/debug-pagealloc: make debug-pagealloc boottime configurable 2014-12-13 12:42:48 -08:00
debug.c mm: make compound_head() robust 2015-11-06 17:50:42 -08:00
dmapool.c mm, page_alloc: distinguish between being unable to sleep, unwilling to sleep and avoiding waking kswapd 2015-11-06 17:50:42 -08:00
early_ioremap.c mm/early_ioremap: use offset_in_page macro 2015-11-05 19:34:48 -08:00
fadvise.c writeback: implement and use inode_congested() 2015-06-02 08:33:35 -06:00
failslab.c mm, page_alloc: rename __GFP_WAIT to __GFP_RECLAIM 2015-11-06 17:50:42 -08:00
filemap.c mm, fs: introduce mapping_gfp_constraint() 2015-11-06 17:50:42 -08:00
frame_vector.c mm: fix docbook comment for get_vaddr_frames() 2015-11-05 19:34:48 -08:00
frontswap.c frontswap: allow multiple backends 2015-06-24 17:49:45 -07:00
gup.c mm: introduce VM_LOCKONFAULT 2015-11-05 19:34:48 -08:00
highmem.c mm/highmem: make kmap cache coloring aware 2014-08-06 18:01:22 -07:00
huge_memory.c mm: loosen MADV_NOHUGEPAGE to enable Qemu postcopy on s390 2015-11-20 16:17:32 -08:00
hugetlb.c mm/hugetlb.c: fix resv map memory leak for placeholder entries 2015-12-12 10:15:34 -08:00
hugetlb_cgroup.c mm: make compound_head() robust 2015-11-06 17:50:42 -08:00
hwpoison-inject.c hwpoison: use page_cgroup_ino for filtering by memcg 2015-09-10 13:29:01 -07:00
init-mm.c
…
internal.h mm: use 'unsigned int' for page order 2015-11-06 17:50:42 -08:00
interval_tree.c mm: replace vma->sharead.linear with vma->shared 2015-02-10 14:30:31 -08:00
kmemcheck.c mm/slab_common: move kmem_cache definition to internal header 2014-10-09 22:25:50 -04:00
kmemleak-test.c mm/kmemleak-test.c: use pr_fmt for logging 2014-06-06 16:08:18 -07:00
kmemleak.c mm/kmemleak.c: remove unneeded initialization of object to NULL 2015-11-05 19:34:48 -08:00
ksm.c ksm: unstable_tree_search_insert error checking cleanup 2015-11-05 19:34:48 -08:00
list_lru.c memcg: simplify and inline __mem_cgroup_from_kmem 2015-11-05 19:34:48 -08:00
maccess.c mm/maccess.c: actually return -EFAULT from strncpy_from_unsafe 2015-11-05 19:34:48 -08:00
madvise.c mm: madvise allow remove operation for hugetlbfs 2015-09-08 15:35:28 -07:00
memblock.c mm/memblock: make memblock_remove_range() static 2015-11-05 19:34:48 -08:00
memcontrol.c mm: memcontrol: fix possible memcg leak due to interrupted reclaim 2015-12-29 17:45:49 -08:00
memory-failure.c mm: make compound_head() robust 2015-11-06 17:50:42 -08:00
memory.c mm, dax: fix DAX deadlocks (COW fault) 2015-11-18 16:54:36 -08:00
memory_hotplug.c mm/memory_hotplug.c: check for missing sections in test_pages_in_a_zone() 2015-12-29 17:45:49 -08:00
mempolicy.c mm: rename alloc_pages_exact_node() to __alloc_pages_node() 2015-09-08 15:35:28 -07:00
mempool.c mm, page_alloc: distinguish between being unable to sleep, unwilling to sleep and avoiding waking kswapd 2015-11-06 17:50:42 -08:00
memtest.c memtest: remove unused header files 2015-09-08 15:35:28 -07:00
migrate.c mm, page_alloc: rename __GFP_WAIT to __GFP_RECLAIM 2015-11-06 17:50:42 -08:00
mincore.c mm/mincore: use offset_in_page macro 2015-11-05 19:34:48 -08:00
mlock.c mm: mlock: add mlock flags to enable VM_LOCKONFAULT usage 2015-11-05 19:34:48 -08:00
mm_init.c mm: meminit: remove mminit_verify_page_links 2015-06-30 19:44:56 -07:00
mmap.c mm: introduce VM_LOCKONFAULT 2015-11-05 19:34:48 -08:00
mmu_context.c sched/mm: call finish_arch_post_lock_switch in idle_task_exit and use_mm 2014-02-21 08:50:17 +01:00
mmu_notifier.c mmu-notifier: add clear_young callback 2015-09-10 13:29:01 -07:00
mmzone.c mm: microoptimize zonelist operations 2015-02-11 17:06:02 -08:00
mprotect.c userfaultfd: teach vma_merge to merge across vma->vm_userfaultfd_ctx 2015-09-04 16:54:41 -07:00
mremap.c mm/mremap: use offset_in_page macro 2015-11-05 19:34:48 -08:00
msync.c mm/msync: use offset_in_page macro 2015-11-05 19:34:48 -08:00
nobootmem.c mm: page_alloc: pass PFN to __free_pages_bootmem 2015-06-30 19:44:55 -07:00
nommu.c mm/nommu.c: drop unlikely inside BUG_ON() 2015-11-05 19:34:48 -08:00
oom_kill.c mm/oom_kill.c: avoid attempting to kill init sharing same memory 2015-12-12 10:15:34 -08:00
page-writeback.c treewide: Remove old email address 2015-11-23 09:44:58 +01:00
page_alloc.c mm: fix swapped Movable and Reclaimable in /proc/pagetypeinfo 2015-12-12 10:15:34 -08:00
page_counter.c mm: page_counter: let page_counter_try_charge() return bool 2015-11-05 19:34:48 -08:00
page_ext.c mm: introduce idle page tracking 2015-09-10 13:29:01 -07:00
page_idle.c mm: introduce idle page tracking 2015-09-10 13:29:01 -07:00
page_io.c fs: use helper bio_add_page() instead of open coding on bi_io_vec 2015-08-13 12:32:00 -06:00
page_isolation.c mm, page_isolation: make set/unset_migratetype_isolate() file-local 2015-09-08 15:35:28 -07:00
page_owner.c mm/page_owner: set correct gfp_mask on page_owner 2015-07-17 16:39:54 -07:00
pagewalk.c mm/pagewalk.c: prevent positive return value of walk_page_test() from being passed to callers 2015-03-25 16:20:30 -07:00
percpu-km.c percpu: implmeent pcpu_nr_empty_pop_pages and chunk->nr_populated 2014-09-02 14:46:05 -04:00
percpu-vm.c percpu: move region iterations out of pcpu_[de]populate_chunk() 2014-09-02 14:46:02 -04:00
percpu.c mm/percpu: use offset_in_page macro 2015-11-05 19:34:48 -08:00
pgtable-generic.c mm,thp: introduce flush_pmd_tlb_range 2015-10-17 17:48:20 +05:30
process_vm_access.c process_vm_access: switch to {compat_,}import_iovec() 2015-04-11 22:27:12 -04:00
quicklist.c
…
readahead.c mm, fs: introduce mapping_gfp_constraint() 2015-11-06 17:50:42 -08:00
rmap.c mm: page migration use migration entry for swapcache too 2015-11-05 19:34:48 -08:00
shmem.c tmpfs: fix shmem_evict_inode() warnings on i_blocks 2015-12-12 10:15:34 -08:00
slab.c slab/slub: adjust kmem_cache_alloc_bulk API 2015-11-22 11:58:44 -08:00
slab.h slab/slub: adjust kmem_cache_alloc_bulk API 2015-11-22 11:58:44 -08:00
slab_common.c slab/slub: adjust kmem_cache_alloc_bulk API 2015-11-22 11:58:44 -08:00
slob.c slab/slub: adjust kmem_cache_alloc_bulk API 2015-11-22 11:58:44 -08:00
slub.c slab/slub: adjust kmem_cache_alloc_bulk API 2015-11-22 11:58:44 -08:00
sparse-vmemmap.c mm/sparse: use memblock apis for early memory allocations 2014-01-21 16:19:47 -08:00
sparse.c mm: use macros from compiler.h instead of __attribute__((...)) 2014-04-07 16:35:54 -07:00
swap.c mm: make compound_head() robust 2015-11-06 17:50:42 -08:00
swap_cgroup.c mm: page_cgroup: rename file to mm/swap_cgroup.c 2014-12-10 17:41:09 -08:00
swap_state.c mm: swap: zswap: maybe_preload & refactoring 2015-09-08 15:35:28 -07:00
swapfile.c mm: /proc/pid/smaps:: show proportional swap share of the mapping 2015-09-08 15:35:28 -07:00
truncate.c memcg: add per cgroup dirty page accounting 2015-06-02 08:33:33 -06:00
userfaultfd.c userfaultfd: avoid mmap_sem read recursion in mcopy_atomic 2015-09-04 16:54:41 -07:00
util.c mm/util: use offset_in_page macro 2015-11-05 19:34:48 -08:00
vmacache.c mm/vmacache: inline vmacache_valid_mm() 2015-11-05 19:34:48 -08:00
vmalloc.c mm: vmalloc: don't remove inexistent guard hole in remove_vm_area() 2015-11-20 16:17:32 -08:00
vmpressure.c mm/vmpressure.c: fix race in vmpressure_work_fn() 2014-12-02 17:32:07 -08:00
vmscan.c mm, page_alloc: distinguish between being unable to sleep, unwilling to sleep and avoiding waking kswapd 2015-11-06 17:50:42 -08:00
vmstat.c vmstat: allocate vmstat_wq before it is used 2016-01-08 23:47:54 -08:00
workingset.c list_lru: add helpers to isolate items 2015-02-12 18:54:10 -08:00
zbud.c mm: zsmalloc: constify struct zs_pool name 2015-11-06 17:50:42 -08:00
zpool.c mm: zsmalloc: constify struct zs_pool name 2015-11-06 17:50:42 -08:00
zsmalloc.c zsmalloc: use page->private instead of page->first_page 2015-11-06 17:50:42 -08:00
zswap.c mm/zswap: change incorrect strncmp use to strcmp 2015-12-18 14:25:40 -08:00