linux-kernel - [PATCH v2 0/4] Fix put_task_struct() calls under PREEMPT

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Message-Id: <20230120150246.20797-1-wander@redhat.com>
Date:   Fri, 20 Jan 2023 12:02:38 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Wander Lairson Costa <wander@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Andrei Vagin <avagin@...il.com>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 0/4] Fix put_task_struct() calls under PREEMPT_RT

put_task_struct() decrements a usage counter and calls
__put_task_struct() if the counter reaches zero.

__put_task_struct() indirectly acquires a spinlock, which is a sleeping
lock under PREEMPT_RT. Therefore, we can't call put_task_struct() in an
atomic context in RT kernels.

This patch series introduces put_task_struct_atomic_safe(), which defers
the call to __put_task_struct() to a process context when compiled with
PREEMPT_RT.

It also fixes known problematic call sites.

Changelog:
==========

v2:
 * Add the put_task_struct_atomic_safe() function that is responsible for
   handling the conditions to call put_task_struct().
 * Replace put_task_struct() by put_task_struct_atomic_safe() in known
   atomic call sites.

Wander Lairson Costa (4):
  sched/task: Add the put_task_struct_atomic_safe function
  sched/deadline: fix inactive_task_timer splat
  sched/rt: use put_task_struct_atomic_safe() to avoid potential splat
  sched/core: use put_task_struct_atomic_safe() to avoid potential splat

 include/linux/sched/task.h | 21 +++++++++++++++++++++
 kernel/fork.c              |  8 ++++++++
 kernel/sched/core.c        |  2 +-
 kernel/sched/deadline.c    |  2 +-
 kernel/sched/rt.c          |  4 ++--
 5 files changed, 33 insertions(+), 4 deletions(-)

-- 
2.39.0