Revert "sched, autogroup: Stop going ahead if autogroup is disabled"
This reverts commit 800d4d30c8.
Between commits 8323f26ce3 ("sched: Fix race in task_group()") and
800d4d30c8 ("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 800d4d30c8 not allowing autogroup to move things, and
commit 8323f26ce3 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: Mike Galbraith <efault@gmx.de>
Acked-by: Ingo 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: Linus Torvalds <torvalds@linux-foundation.org>
fd8ef11730