• Michal Hocko's avatar
    vmstat: allocate vmstat_wq before it is used · 751e5f5c
    Michal Hocko authored
    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-g373ccbe5 #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: 373ccbe5 ("mm, vmstat: allow WQ concurrency to discover memory reclaim doesn't make any progress")
    Reported-by: default avatarkernel test robot <ying.huang@linux.intel.com>
    Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
    Tested-by: default avatarTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
    Cc: stable@vger.kernel.org
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    751e5f5c
vmstat.c 41.3 KB