# git rev-parse -q --verify 751e5f5c753e8d447bcf89f9e96b9616ac081628^{commit}
751e5f5c753e8d447bcf89f9e96b9616ac081628
already have revision, skipping fetch
# git checkout -q -f -B kisskb 751e5f5c753e8d447bcf89f9e96b9616ac081628
# git clean -qxdf
# git log -1
commit 751e5f5c753e8d447bcf89f9e96b9616ac081628
Author: Michal Hocko <mhocko@suse.com>
Date:   Fri Jan 8 11:18:29 2016 +0100

    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: 373ccbe59270 ("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>
# < /opt/cross/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc --version
# < git log --format=%s --max-count=1 751e5f5c753e8d447bcf89f9e96b9616ac081628
# < make -j 240 ARCH=arm O=/home/kisskb/slave/build/linus_arm-randconfig_arm CROSS_COMPILE=/opt/cross/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-  randconfig
KCONFIG_SEED=0xE86CEF50
warning: (ARCH_INTEGRATOR && ARCH_MULTIPLATFORM && ARCH_EP93XX) selects ARM_PATCH_PHYS_VIRT which has unmet direct dependencies (!XIP_KERNEL && MMU && (!ARCH_REALVIEW || !SPARSEMEM))
# make -j 240 ARCH=arm O=/home/kisskb/slave/build/linus_arm-randconfig_arm CROSS_COMPILE=/opt/cross/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-  
make[1]: Entering directory `/home/kisskb/slave/build/linus_arm-randconfig_arm'
  GEN     ./Makefile
scripts/kconfig/conf  --silentoldconfig Kconfig
.config:330:warning: symbol value '' invalid for PAGE_OFFSET
warning: (ARCH_INTEGRATOR && ARCH_MULTIPLATFORM && ARCH_EP93XX) selects ARM_PATCH_PHYS_VIRT which has unmet direct dependencies (!XIP_KERNEL && MMU && (!ARCH_REALVIEW || !SPARSEMEM))
warning: (ARCH_INTEGRATOR && ARCH_MULTIPLATFORM && ARCH_EP93XX) selects ARM_PATCH_PHYS_VIRT which has unmet direct dependencies (!XIP_KERNEL && MMU && (!ARCH_REALVIEW || !SPARSEMEM))
#
# configuration written to .config
#
make[1]: Leaving directory `/home/kisskb/slave/build/linus_arm-randconfig_arm'
make[1]: Entering directory `/home/kisskb/slave/build/linus_arm-randconfig_arm'
  CHK     include/config/kernel.release
  GEN     ./Makefile
  WRAP    arch/arm/include/generated/asm/bitsperlong.h
  WRAP    arch/arm/include/generated/asm/cputime.h
  WRAP    arch/arm/include/generated/asm/current.h
  WRAP    arch/arm/include/generated/asm/emergency-restart.h
  WRAP    arch/arm/include/generated/asm/errno.h
  WRAP    arch/arm/include/generated/asm/exec.h
  WRAP    arch/arm/include/generated/asm/ioctl.h
  WRAP    arch/arm/include/generated/asm/ipcbuf.h
  WRAP    arch/arm/include/generated/asm/irq_regs.h
  CHK     include/generated/uapi/linux/version.h
  WRAP    arch/arm/include/generated/asm/kdebug.h
  WRAP    arch/arm/include/generated/asm/local.h
  WRAP    arch/arm/include/generated/asm/local64.h
  WRAP    arch/arm/include/generated/asm/mm-arch-hooks.h
  WRAP    arch/arm/include/generated/asm/msgbuf.h
  UPD     include/generated/uapi/linux/version.h
  WRAP    arch/arm/include/generated/asm/msi.h
  WRAP    arch/arm/include/generated/asm/param.h
  WRAP    arch/arm/include/generated/asm/parport.h
  WRAP    arch/arm/include/generated/asm/poll.h
  WRAP    arch/arm/include/generated/asm/preempt.h
  WRAP    arch/arm/include/generated/asm/resource.h
  WRAP    arch/arm/include/generated/asm/rwsem.h
  WRAP    arch/arm/include/generated/asm/seccomp.h
  WRAP    arch/arm/include/generated/asm/sections.h
  WRAP    arch/arm/include/generated/asm/segment.h
  WRAP    arch/arm/include/generated/asm/sembuf.h
  WRAP    arch/arm/include/generated/asm/serial.h
  WRAP    arch/arm/include/generated/asm/shmbuf.h
  WRAP    arch/arm/include/generated/asm/siginfo.h
  WRAP    arch/arm/include/generated/asm/sizes.h
  WRAP    arch/arm/include/generated/asm/simd.h
  WRAP    arch/arm/include/generated/asm/socket.h
  WRAP    arch/arm/include/generated/asm/sockios.h
  UPD     include/config/kernel.release
  WRAP    arch/arm/include/generated/asm/termbits.h
  WRAP    arch/arm/include/generated/asm/termios.h
  WRAP    arch/arm/include/generated/asm/timex.h
  WRAP    arch/arm/include/generated/asm/trace_clock.h
  WRAP    arch/arm/include/generated/asm/unaligned.h
  HOSTCC  scripts/basic/bin2c
  Using /home/kisskb/slave/src as source for kernel
  CHK     include/generated/utsrelease.h
  UPD     include/generated/utsrelease.h
  Generating include/generated/mach-types.h
  HOSTCC  scripts/kallsyms
  HOSTCC  scripts/pnmtologo
  HOSTCC  scripts/conmakehash
  CC      scripts/mod/empty.o
  HOSTCC  scripts/mod/mk_elfconfig
  CC      scripts/mod/devicetable-offsets.s
  CHK     include/generated/timeconst.h
  CC      kernel/bounds.s
  UPD     include/generated/timeconst.h
  CHK     include/generated/bounds.h
  UPD     include/generated/bounds.h
  CC      arch/arm/kernel/asm-offsets.s
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  HOSTCC  scripts/mod/sumversion.o
  GEN     scripts/mod/devicetable-offsets.h
  HOSTCC  scripts/mod/file2alias.o
In file included from /home/kisskb/slave/src/arch/arm/kernel/asm-offsets.c:15:0:
/home/kisskb/slave/src/include/linux/mm.h: In function 'virt_to_head_page':
/home/kisskb/slave/src/include/linux/mm.h:502:1: error: invalid suffix "xUL" on integer constant
In file included from /home/kisskb/slave/src/include/linux/dma-mapping.h:10:0,
                 from /home/kisskb/slave/src/arch/arm/kernel/asm-offsets.c:16:
/home/kisskb/slave/src/include/linux/scatterlist.h: In function 'sg_set_buf':
/home/kisskb/slave/src/include/linux/scatterlist.h:140:1: error: invalid suffix "xUL" on integer constant
/home/kisskb/slave/src/include/linux/scatterlist.h:140:1: error: invalid suffix "xUL" on integer constant
/home/kisskb/slave/src/include/linux/scatterlist.h:142:1: error: invalid suffix "xUL" on integer constant
In file included from /home/kisskb/slave/src/arch/arm/include/asm/dma-mapping.h:49:0,
                 from /home/kisskb/slave/src/include/linux/dma-mapping.h:87,
                 from /home/kisskb/slave/src/arch/arm/kernel/asm-offsets.c:16:
/home/kisskb/slave/src/include/asm-generic/dma-mapping-common.h: In function 'dma_map_single_attrs':
/home/kisskb/slave/src/include/asm-generic/dma-mapping-common.h:21:1: error: invalid suffix "xUL" on integer constant
/home/kisskb/slave/src/include/asm-generic/dma-mapping-common.h:24:1: error: invalid suffix "xUL" on integer constant
In file included from /home/kisskb/slave/src/include/linux/dma-mapping.h:87:0,
                 from /home/kisskb/slave/src/arch/arm/kernel/asm-offsets.c:16:
/home/kisskb/slave/src/arch/arm/include/asm/dma-mapping.h: In function 'virt_to_dma':
/home/kisskb/slave/src/arch/arm/include/asm/dma-mapping.h:92:1: error: invalid suffix "xUL" on integer constant
make[2]: *** [arch/arm/kernel/asm-offsets.s] Error 1
make[1]: *** [prepare0] Error 2
make[1]: *** Waiting for unfinished jobs....
  HOSTLD  scripts/mod/modpost
make[1]: Leaving directory `/home/kisskb/slave/build/linus_arm-randconfig_arm'
make: *** [sub-make] Error 2
Command 'make -j 240 ARCH=arm O=/home/kisskb/slave/build/linus_arm-randconfig_arm CROSS_COMPILE=/opt/cross/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-  ' returned non-zero exit status 2
# rm -rf /home/kisskb/slave/build/linus_arm-randconfig_arm
# Build took: 0:00:05.081485