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From:   Aubrey Li <aubrey.intel@gmail.com>
Date:   Wed, 24 Apr 2019 07:25:41 +0800
Message-ID: <CAERHkrtcW8L0duMTzkt-eDnesiG6sEO=zfswZcoM+n3TMxrG_w@mail.gmail.com>
Subject: Re: [RFC PATCH v2 00/17] Core scheduling v2
To:     Vineeth Remanan Pillai <vpillai@digitalocean.com>
Cc:     Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul Turner <pjt@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Subhra Mazumdar <subhra.mazumdar@oracle.com>,
        =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= <fweisbec@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Greg Kerr <kerrnel@google.com>, Phil Auld <pauld@redhat.com>,
        Aaron Lu <aaron.lwe@gmail.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>
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On Wed, Apr 24, 2019 at 12:18 AM Vineeth Remanan Pillai
<vpillai@digitalocean.com> wrote:
>
> Second iteration of the core-scheduling feature.
>
> This version fixes apparent bugs and performance issues in v1. This
> doesn't fully address the issue of core sharing between processes
> with different tags. Core sharing still happens 1% to 5% of the time
> based on the nature of workload and timing of the runnable processes.
>
> Changes in v2
> -------------
> - rebased on mainline commit: 6d906f99817951e2257d577656899da02bb33105
> - Fixes for couple of NULL pointer dereference crashes
>   - Subhra Mazumdar
>   - Tim Chen

Is this one missed? Or fixed with a better impl?

The boot up CPUs don't match the possible cpu map, so the not onlined
CPU rq->core are not initialized, which causes NULL pointer dereference
panic in online_fair_sched_group():

Thanks,
-Aubrey

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 85c728d..bdabf20 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10492,6 +10492,10 @@ void online_fair_sched_group(struct task_group *tg)
                rq = cpu_rq(i);
                se = tg->se[i];

+#ifdef CONFIG_SCHED_CORE
+               if (!rq->core)
+                       continue;
+#endif
                raw_spin_lock_irq(rq_lockp(rq));
                update_rq_clock(rq);
                attach_entity_cfs_rq(se);

> - Improves priority comparison logic for process in different cpus
>   - Peter Zijlstra
>   - Aaron Lu
> - Fixes a hard lockup in rq locking
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fixes a performance issue seen on IO heavy workloads
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fix for 32bit build
>   - Aubrey Li
>
> Issues
> ------
> - Processes with different tags can still share the core
> - A crash when disabling cpus with core-scheduling on
>    - https://paste.debian.net/plainh/fa6bcfa8
>
> ---
>
> Peter Zijlstra (16):
>   stop_machine: Fix stop_cpus_in_progress ordering
>   sched: Fix kerneldoc comment for ia64_set_curr_task
>   sched: Wrap rq::lock access
>   sched/{rt,deadline}: Fix set_next_task vs pick_next_task
>   sched: Add task_struct pointer to sched_class::set_curr_task
>   sched/fair: Export newidle_balance()
>   sched: Allow put_prev_task() to drop rq->lock
>   sched: Rework pick_next_task() slow-path
>   sched: Introduce sched_class::pick_task()
>   sched: Core-wide rq->lock
>   sched: Basic tracking of matching tasks
>   sched: A quick and dirty cgroup tagging interface
>   sched: Add core wide task selection and scheduling.
>   sched/fair: Add a few assertions
>   sched: Trivial forced-newidle balancer
>   sched: Debug bits...
>
> Vineeth Remanan Pillai (1):
>   sched: Wake up sibling if it has something to run
>
>  include/linux/sched.h    |   9 +-
>  kernel/Kconfig.preempt   |   7 +-
>  kernel/sched/core.c      | 800 +++++++++++++++++++++++++++++++++++++--
>  kernel/sched/cpuacct.c   |  12 +-
>  kernel/sched/deadline.c  |  99 +++--
>  kernel/sched/debug.c     |   4 +-
>  kernel/sched/fair.c      | 137 +++++--
>  kernel/sched/idle.c      |  42 +-
>  kernel/sched/pelt.h      |   2 +-
>  kernel/sched/rt.c        |  96 +++--
>  kernel/sched/sched.h     | 185 ++++++---
>  kernel/sched/stop_task.c |  35 +-
>  kernel/sched/topology.c  |   4 +-
>  kernel/stop_machine.c    |   2 +
>  14 files changed, 1145 insertions(+), 289 deletions(-)
>
> --
> 2.17.1
>