• Mike Galbraith's avatar
    Revert "sched, autogroup: Stop going ahead if autogroup is disabled" · fd8ef117
    Mike Galbraith authored
    This reverts commit 800d4d30.
    
    Between commits 8323f26c ("sched: Fix race in task_group()") and
    800d4d30 ("sched, autogroup: Stop going ahead if autogroup is
    disabled"), autogroup is a wreck.
    
    With both applied, all you have to do to crash a box is disable
    autogroup during boot up, then reboot..  boom, NULL pointer dereference
    due to commit 800d4d30 not allowing autogroup to move things, and
    commit 8323f26c making that the only way to switch runqueues:
    
      BUG: unable to handle kernel NULL pointer dereference at           (null)
      IP: [<ffffffff81063ac0>] effective_load.isra.43+0x50/0x90
      Pid: 7047, comm: systemd-user-se Not tainted 3.6.8-smp #7 MEDIONPC MS-7502/MS-7502
      RIP: effective_load.isra.43+0x50/0x90
      Process systemd-user-se (pid: 7047, threadinfo ffff880221dde000, task ffff88022618b3a0)
      Call Trace:
        select_task_rq_fair+0x255/0x780
        try_to_wake_up+0x156/0x2c0
        wake_up_state+0xb/0x10
        signal_wake_up+0x28/0x40
        complete_signal+0x1d6/0x250
        __send_signal+0x170/0x310
        send_signal+0x40/0x80
        do_send_sig_info+0x47/0x90
        group_send_sig_info+0x4a/0x70
        kill_pid_info+0x3a/0x60
        sys_kill+0x97/0x1a0
        ? vfs_read+0x120/0x160
        ? sys_read+0x45/0x90
        system_call_fastpath+0x16/0x1b
      Code: 49 0f af 41 50 31 d2 49 f7 f0 48 83 f8 01 48 0f 46 c6 48 2b 07 48 8b bf 40 01 00 00 48 85 ff 74 3a 45 31 c0 48 8b 8f 50 01 00 00 <48> 8b 11 4c 8b 89 80 00 00 00 49 89 d2 48 01 d0 45 8b 59 58 4c
      RIP  [<ffffffff81063ac0>] effective_load.isra.43+0x50/0x90
       RSP <ffff880221ddfbd8>
      CR2: 0000000000000000
    Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
    Acked-by: default avatarIngo Molnar <mingo@kernel.org>
    Cc: Yong Zhang <yong.zhang0@gmail.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: stable@vger.kernel.org # 2.6.39+
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    fd8ef117
auto_group.c 5.54 KB