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Message-ID: <2023040343-dingbat-undermine-3b2d@gregkh>
Date: Mon, 3 Apr 2023 15:30:51 +0200
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 v2 4.19 0/3] Backport patches to fix threadgroup_rwsem
<-> cpus_read_lock() deadlock
On Mon, Mar 20, 2023 at 01:15:04AM +0000, Cai Xinchen wrote:
> I am very sorry. My gcc version is 7.5 and it does not report error.
>
> 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")
>
> Changes in v2:
> * Add #include <linux/cpu.h> in kernel/cgroup/cgroup.c to
> avoid some compile error.
> * Exchange get_online_cpus() location in cpuset_attach to
> keep cpu_hotplug_lock->cpuset_mutex order, although it will
> be remove by ("cgroup: Fix threadgroup_rwsem <->
> cpus_read_lock() deadlock")
>
> 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 | 50 +++++++++++++++++++++++++++++++++++----
> kernel/cgroup/cpuset.c | 25 ++++++++++++--------
> 4 files changed, 67 insertions(+), 19 deletions(-)
Now queued up, thanks.
greg k-h
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