linux-kernel - [PATCH v2 0/4] sched/fair: Active balancer RT/DL preemption fix

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20190815145107.5318-1-valentin.schneider@arm.com>
Date:   Thu, 15 Aug 2019 15:51:03 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org,
        tglx@...utronix.de, qais.yousef@....com
Subject: [PATCH v2 0/4] sched/fair: Active balancer RT/DL preemption fix

Vincent's load balance rework [1] got me thinking about how and where we
use rq.nr_running vs rq.cfs.h_nr_running checks, and this lead me to
stare intently at the active load balancer.

I haven't seen it happen (yet), but from reading the code it really looks
like we can have some scenarios where the cpu_stopper ends up preempting
a > CFS class task, since we never actually look at what's the remote rq's
running task.

This series shuffles things around the CFS active load balancer to prevent
this from happening.

- Patch 1 is a freebie cleanup
- Patch 2 is a preparatory code move
- Patch 3 adds h_nr_running checks
- Patch 4 adds a sched class check + detach_one_task() to the active balance

This is based on top of today's tip/sched/core:
  a46d14eca7b7 ("sched/fair: Use rq_lock/unlock in online_fair_sched_group")

v1 -> v2:
  - (new patch) Added need_active_balance() cleanup

  - Tweaked active balance code move to respect existing
    sd->nr_balance_failed modifications
  - Added explicit checks of active_load_balance()'s return value
  
  - Added an h_nr_running < 1 check before kicking the cpu_stopper

  - Added a detach_one_task() call in active_load_balance() when the remote
    rq's running task is > CFS

[1]: https://lore.kernel.org/lkml/1564670424-26023-1-git-send-email-vincent.guittot@linaro.org/

Valentin Schneider (4):
  sched/fair: Make need_active_balance() return bools
  sched/fair: Move active balance logic to its own function
  sched/fair: Check for CFS tasks before detach_one_task()
  sched/fair: Prevent active LB from preempting higher sched classes

 kernel/sched/fair.c | 151 ++++++++++++++++++++++++++++----------------
 1 file changed, 95 insertions(+), 56 deletions(-)

--
2.22.0