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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 <[email protected]>
Signed-off-by: Michal Hocko <[email protected]>
Tested-by: Tetsuo Handa <[email protected]>
Cc: [email protected]
Cc: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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
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_debug.c
mm/cma_debug: correct size input to bitmap function
2015-07-17 16:39:54 -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
compaction.c
mm, compaction: distinguish contended status in tracepoints
2015-11-05 19:34:48 -08:00
debug-pagealloc.c
…
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
…
huge_memory.c
mm: loosen MADV_NOHUGEPAGE to enable Qemu postcopy on s390
2015-11-20 16:17:32 -08:00
hugetlb_cgroup.c
mm: make compound_head() robust
2015-11-06 17:50:42 -08:00
hugetlb.c
mm/hugetlb.c: fix resv map memory leak for placeholder entries
2015-12-12 10:15:34 -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
…
Kconfig
mm: make compound_head() robust
2015-11-06 17:50:42 -08:00
Kconfig.debug
…
kmemcheck.c
…
kmemleak-test.c
…
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
Makefile
Merge tag 'media/v4.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
2015-09-11 16:42:39 -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_hotplug.c
mm/memory_hotplug.c: check for missing sections in test_pages_in_a_zone()
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
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
…
mmu_notifier.c
mmu-notifier: add clear_young callback
2015-09-10 13:29:01 -07:00
mmzone.c
…
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_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
page-writeback.c
treewide: Remove old email address
2015-11-23 09:44:58 +01:00
pagewalk.c
…
percpu-km.c
…
percpu-vm.c
…
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_common.c
slab/slub: adjust kmem_cache_alloc_bulk API
2015-11-22 11:58:44 -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
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
…
sparse.c
…
swap_cgroup.c
…
swap_state.c
mm: swap: zswap: maybe_preload & refactoring
2015-09-08 15:35:28 -07:00
swap.c
mm: make compound_head() robust
2015-11-06 17:50:42 -08:00
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
…
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
…
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