Re: [PATCH v4 0/3] Fix deadlock caused by cgroup_mutex and cpu_hotplug_lock

From: Chen Ridong
Date: Fri Sep 20 2024 - 22:06:56 EST




On 2024/9/21 3:23, Tejun Heo wrote:
On Wed, Sep 18, 2024 at 05:44:47PM +0800, Chen Ridong wrote:
...
cgroup: fix deadlock caused by cgroup_mutex and cpu_hotplug_lock
workqueue: doc: Add a note saturating the system_wq is not permitted
workqueue: Adjust WQ_MAX_ACTIVE from 512 to 2048

Documentation/core-api/workqueue.rst | 8 ++++++--
include/linux/workqueue.h | 2 +-
kernel/bpf/cgroup.c | 2 +-
kernel/cgroup/cgroup-internal.h | 1 +
kernel/cgroup/cgroup.c | 2 +-
5 files changed, 10 insertions(+), 5 deletions(-)

Friendly ping.

I don't know why but this series isn't in my inbox for some reason. Here are
some feedbacks after looking at the thread from lore:

- Can you create a separate workqueue for cgrp->bpf.release_work instead of
exporting cgroup_destroy_wq? Workqueues aren't that expensive. No reason
to share like this.

- The patch title is rather misleading. The deadlock isn't really caused
between cgroup_mutex and cpu_hotplug_lock. They're just victims of
system_wq concurrency depletion. Can you please update accordingly?

- Can you add a new line before the note paragraph? Also, I'd say "deadlock"
rather than "block" to properly convey the imapct of such saturation
events. I don't think "eg. cgroup release work" is adding much.

Thanks.


Thanks, TJ, I will do that.

Best regards,
Ridong