# 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/i386-linux/bin/i386-linux-gcc --version
# < git log --format=%s --max-count=1 751e5f5c753e8d447bcf89f9e96b9616ac081628
# < make -j 48 ARCH=i386 O=/home/kisskb/slave/build/linus_i386-randconfig_i386 CROSS_COMPILE=/opt/cross/gcc-4.6.3-nolibc/i386-linux/bin/i386-linux-  randconfig
KCONFIG_SEED=0x38DB4AFD
# Added to kconfig CONFIG_STANDALONE=y
# yes \n | make -j 48 ARCH=i386 O=/home/kisskb/slave/build/linus_i386-randconfig_i386 CROSS_COMPILE=/opt/cross/gcc-4.6.3-nolibc/i386-linux/bin/i386-linux-  oldconfig
yes: standard output: Broken pipe
yes: write error
# make -j 48 ARCH=i386 O=/home/kisskb/slave/build/linus_i386-randconfig_i386 CROSS_COMPILE=/opt/cross/gcc-4.6.3-nolibc/i386-linux/bin/i386-linux-  
make[1]: Entering directory '/home/kisskb/slave/build/linus_i386-randconfig_i386'
  GEN     ./Makefile
scripts/kconfig/conf  --silentoldconfig Kconfig
arch/x86/Makefile:133: stack-protector enabled but compiler support broken
/home/kisskb/slave/src/Makefile:660: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong not supported by compiler
  SYSTBL  arch/x86/entry/syscalls/../../include/generated/asm/syscalls_32.h
  SYSHDR  arch/x86/entry/syscalls/../../include/generated/uapi/asm/unistd_32.h
  SYSHDR  arch/x86/entry/syscalls/../../include/generated/uapi/asm/unistd_64.h
  SYSHDR  arch/x86/entry/syscalls/../../include/generated/uapi/asm/unistd_x32.h
  HOSTCC  scripts/basic/bin2c
  CHK     include/config/kernel.release
  GEN     ./Makefile
  WRAP    arch/x86/include/generated/asm/clkdev.h
  WRAP    arch/x86/include/generated/asm/cputime.h
  WRAP    arch/x86/include/generated/asm/dma-contiguous.h
  WRAP    arch/x86/include/generated/asm/early_ioremap.h
  WRAP    arch/x86/include/generated/asm/mcs_spinlock.h
  WRAP    arch/x86/include/generated/asm/mm-arch-hooks.h
  CHK     include/generated/uapi/linux/version.h
  UPD     include/generated/uapi/linux/version.h
  HOSTCC  scripts/kallsyms
  HOSTCC  scripts/conmakehash
  HOSTCC  scripts/sortextable
  HOSTCC  scripts/asn1_compiler
  HOSTCC  scripts/extract-cert
  HOSTCC  scripts/pnmtologo
  UPD     include/config/kernel.release
  CC      scripts/mod/empty.o
  HOSTCC  scripts/mod/mk_elfconfig
cc1: error: unrecognized command line option '-fstack-protector-strong'
  CC      scripts/mod/devicetable-offsets.s
/home/kisskb/slave/src/scripts/Makefile.build:258: recipe for target 'scripts/mod/empty.o' failed
cc1: error: unrecognized command line option '-fstack-protector-strong'make[3]: *** [scripts/mod/empty.o] Error 1

make[3]: *** Waiting for unfinished jobs....
/home/kisskb/slave/src/scripts/Makefile.build:153: recipe for target 'scripts/mod/devicetable-offsets.s' failed
make[3]: *** [scripts/mod/devicetable-offsets.s] Error 1
  HOSTCC  arch/x86/tools/relocs_32.o
  HOSTCC  arch/x86/tools/relocs_64.o
  HOSTCC  arch/x86/tools/relocs_common.o
  Using /home/kisskb/slave/src as source for kernel
/home/kisskb/slave/src/scripts/Makefile.build:403: recipe for target 'scripts/mod' failed
make[2]: *** [scripts/mod] Error 2
make[2]: *** Waiting for unfinished jobs....
  CHK     include/generated/utsrelease.h
  UPD     include/generated/utsrelease.h
  HOSTLD  arch/x86/tools/relocs
/home/kisskb/slave/src/Makefile:545: recipe for target 'scripts' failed
make[1]: *** [scripts] Error 2
make[1]: *** Waiting for unfinished jobs....
make[1]: Leaving directory '/home/kisskb/slave/build/linus_i386-randconfig_i386'
Makefile:146: recipe for target 'sub-make' failed
make: *** [sub-make] Error 2
Command 'make -j 48 ARCH=i386 O=/home/kisskb/slave/build/linus_i386-randconfig_i386 CROSS_COMPILE=/opt/cross/gcc-4.6.3-nolibc/i386-linux/bin/i386-linux-  ' returned non-zero exit status 2
# rm -rf /home/kisskb/slave/build/linus_i386-randconfig_i386
# Build took: 0:00:04.544901