linux-kernel - Re: [PATCH 4.19 0/3] Backport patches to fix threadgroup_rwsem <-> cpus_read

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Message-ID: <ZBLJDrkjFfLif6ZX@kroah.com>
Date:   Thu, 16 Mar 2023 08:45:18 +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(-)

This series breaks the build on many architectures, so I will now have
to go drop them from the 4.19.y queue.  Please fix up and resubmit if
you wish to have them applied in the future.

thanks,

greg k-h