4.4-stable review patch. If anyone has any objections, please let me know.
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From: Ethan Zhao ethan.zhao@oracle.com
commit 5ccba44ba118a5000cccc50076b0344632459779 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: James Puthukattukaran james.puthukattukaran@oracle.com Signed-off-by: Ethan Zhao ethan.zhao@oracle.com Signed-off-by: Peter 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... Signed-off-by: Ingo Molnar mingo@kernel.org Cc: Steve Muckle smuckle@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/sysctl.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -342,7 +342,8 @@ static struct ctl_table kern_table[] = { .data = &sysctl_sched_time_avg, .maxlen = sizeof(unsigned int), .mode = 0644, - .proc_handler = proc_dointvec, + .proc_handler = proc_dointvec_minmax, + .extra1 = &one, }, { .procname = "sched_shares_window_ns",