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Message-ID: <ZBGCEgB7wEe0pCNk@kroah.com>
Date: Wed, 15 Mar 2023 09:30:10 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Cai Xinchen <caixinchen1@...wei.com>
Cc: longman@...hat.com, lizefan.x@...edance.com, tj@...nel.org,
hannes@...xchg.org, sashal@...nel.org, mkoutny@...e.com,
zhangqiao22@...wei.com, juri.lelli@...hat.com,
penguin-kernel@...ove.sakura.ne.jp, stable@...r.kernel.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.19 0/3] Backport patches to fix threadgroup_rwsem <->
cpus_read_lock() deadlock
On Fri, Mar 03, 2023 at 04:50:47AM +0000, Cai Xinchen wrote:
> We have a deadlock problem which can be solved by commit 4f7e7236435ca
> ("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock").
> However, it makes lock order of cpus_read_lock and cpuset_mutex
> wrong in v4.19. The call sequence is as follows:
> cgroup_procs_write()
> cgroup_procs_write_start()
> get_online_cpus(); // cpus_read_lock()
> percpu_down_write(&cgroup_threadgroup_rwsem)
> cgroup_attach_task
> cgroup_migrate
> cgroup_migrate_execute
> ss->attach (cpust_attach)
> mutex_lock(&cpuset_mutex)
>
> it seems hard to make cpus_read_lock is locked before
> cgroup_threadgroup_rwsem and cpuset_mutex is locked before
> cpus_read_lock unless backport the commit d74b27d63a8beb
> ("cgroup/cpuset: Change cpuset_rwsem and hotplug lock order")
>
> Juri Lelli (1):
> cgroup/cpuset: Change cpuset_rwsem and hotplug lock order
>
> Tejun Heo (1):
> cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock
>
> Tetsuo Handa (1):
> cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()
>
> include/linux/cpuset.h | 8 +++----
> kernel/cgroup/cgroup-v1.c | 3 +++
> kernel/cgroup/cgroup.c | 49 +++++++++++++++++++++++++++++++++++----
> kernel/cgroup/cpuset.c | 25 ++++++++++++--------
> 4 files changed, 66 insertions(+), 19 deletions(-)
>
> --
> 2.17.1
>
Now queued up, thanks.
greg k-h
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