linux-kernel - [RFC PATCH v2 0/2] workqueue: destroy

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Message-Id: <20220727115327.2273547-1-vschneid@redhat.com>
Date:   Wed, 27 Jul 2022 12:53:25 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Phil Auld <pauld@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: [RFC PATCH v2 0/2] workqueue: destroy_worker() vs isolated CPUs

Hi folks,

Using a work struct from within the workqueue code itself is a bit scary, but
I've done more rigorous testing than for v1 and it's looking OK (at the very
least locking-wise).

Note that this affects all kworkers (not just percpu ones) for the sake of
consistency and to prevent adding extra corner cases. kthread_set_per_cpu(p, -1)
is a no-op for unbound kworkers, and IIUC the affinity change is not required
since unbound workers have to be affined to a subset of wq_unbound_cpumask, but
it shouldn't be harmful either.

2/2 is a simple and stupid stresser that forces extra pcpu kworkers to be
spawned on a specific CPU - I can then quickly test this on QEMU by making sure
said CPU is isolated on the cmdline.

Thanks to Tejun & Lai for the discussion thus far.

Revisions
=========

RFCv1 -> RFCv2
++++++++++++++

o Change the pool->timer into a delayed_work to have a sleepable context for
  unbinding kworkers

Cheers,
Valentin

Valentin Schneider (2):
  workqueue: Unbind workers before sending them to exit()
  DEBUG: workqueue: kworker spawner

 kernel/Makefile    |   2 +-
 kernel/workqueue.c | 118 ++++++++++++++++++++++++++++++++++-----------
 kernel/wqstress.c  |  69 ++++++++++++++++++++++++++
 3 files changed, 159 insertions(+), 30 deletions(-)
 create mode 100644 kernel/wqstress.c

--
2.31.1