• Ethan Zhao's avatar
    sched/sysctl: Check user input value of sysctl_sched_time_avg · 21a24b5d
    Ethan Zhao authored
    commit 5ccba44b upstream.
    
    System will hang if user set sysctl_sched_time_avg to 0:
    
      [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0
    
      Stack traceback for pid 0
      0xffff883f6406c600 0 0 1 3 R 0xffff883f6406cf50 *swapper/3
      ffff883f7ccc3ae8 0000000000000018 ffffffff810c4dd0 0000000000000000
      0000000000017800 ffff883f7ccc3d78 0000000000000003 ffff883f7ccc3bf8
      ffffffff810c4fc9 ffff883f7ccc3c08 00000000810c5043 ffff883f7ccc3c08
      Call Trace:
      <IRQ> [<ffffffff810c4dd0>] ? update_group_capacity+0x110/0x200
      [<ffffffff810c4fc9>] ? update_sd_lb_stats+0x109/0x600
      [<ffffffff810c5507>] ? find_busiest_group+0x47/0x530
      [<ffffffff810c5b84>] ? load_balance+0x194/0x900
      [<ffffffff810ad5ca>] ? update_rq_clock.part.83+0x1a/0xe0
      [<ffffffff810c6d42>] ? rebalance_domains+0x152/0x290
      [<ffffffff810c6f5c>] ? run_rebalance_domains+0xdc/0x1d0
      [<ffffffff8108a75b>] ? __do_softirq+0xfb/0x320
      [<ffffffff8108ac85>] ? irq_exit+0x125/0x130
      [<ffffffff810b3a17>] ? scheduler_ipi+0x97/0x160
      [<ffffffff81052709>] ? smp_reschedule_interrupt+0x29/0x30
      [<ffffffff8173a1be>] ? reschedule_interrupt+0x6e/0x80
       <EOI> [<ffffffff815bc83c>] ? cpuidle_enter_state+0xcc/0x230
      [<ffffffff815bc80c>] ? cpuidle_enter_state+0x9c/0x230
      [<ffffffff815bc9d7>] ? cpuidle_enter+0x17/0x20
      [<ffffffff810cd6dc>] ? cpu_startup_entry+0x38c/0x420
      [<ffffffff81053373>] ? start_secondary+0x173/0x1e0
    
    Because divide-by-zero error happens in function:
    
    update_group_capacity()
      update_cpu_capacity()
        scale_rt_capacity()
         {
              ...
              total = sched_avg_period() + delta;
              used = div_u64(avg, total);
              ...
         }
    
    To fix this issue, check user input value of sysctl_sched_time_avg, keep
    it unchanged when hitting invalid input, and set the minimum limit of
    sysctl_sched_time_avg to 1 ms.
    Reported-by: default avatarJames Puthukattukaran <james.puthukattukaran@oracle.com>
    Signed-off-by: default avatarEthan Zhao <ethan.zhao@oracle.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: efault@gmx.de
    Cc: ethan.kernel@gmail.com
    Cc: keescook@chromium.org
    Cc: mcgrof@kernel.org
    Cc: <stable@vger.kernel.org>
    Link: http://lkml.kernel.org/r/1504504774-18253-1-git-send-email-ethan.zhao@oracle.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Cc: Steve Muckle <smuckle@google.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    21a24b5d
sysctl.c 66 KB