Messages in this thread | | | Date | Wed, 20 Jul 2022 16:36:50 +0530 | Subject | Re: Query regarding deadlock involving cgroup_threadgroup_rwsem and cpu_hotplug_lock | From | Mukesh Ojha <> |
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Hi,
On 7/20/2022 8:57 AM, Imran Khan wrote: > Hello everyone, > > I am seeing a deadlock between cgroup_threadgroup_rwsem and cpu_hotplug_lock in > 5.4 kernel. > > Due to some missing drivers I don't have this test setup for latest upstream > kernel but looking at the code the issue seems to be present in the latest > kernel as well. If needed I can provide stack traces and other relevant info > from the vmcore that I have got from 5.4 setup. > > The description of the problem is as follows (I am using 5.19-rc7 as reference > below): > > __cgroup_procs_write acquires cgroup_threadgroup_rwsem via > cgroup_procs_write_start and then invokes cgroup_attach_task. Now > cgroup_attach_task can invoke following call chain: > > cgroup_attach_task --> cgroup_migrate --> cgroup_migrate_execute --> cpuset_attach > > Here cpuset_attach tries to take cpu_hotplug_lock. > > But by this time if some other context > > 1. is already in the middle of cpu hotplug and has acquired cpu_hotplug_lock in > _cpu_up but > 2. has not yet reached CPUHP_ONLINE state and > 3. one of the intermediate hotplug states (in my case CPUHP_AP_ONLINE_DYN ) has > a callback which involves creation of a thread (or invocation of copy_process > via some other path) the invoked copy_process will get blocked on > cgroup_threadgroup_rwsem in following call chain: > > copy_process --> cgroup_can_fork --> cgroup_css_set_fork --> > cgroup_threadgroup_change_begin
Similar discussion is at [1], not sure on the conclusion.
[1] https://lore.kernel.org/lkml/20220705123705.764-1-xuewen.yan@unisoc.com/
-Mukesh
> > > I am looking for suggestions to fix this deadlock. > > Or if I am missing something in the above analysis and the above mention > scenario can't happen in latest upstream kernel, then please let me know as that > would help me in back porting relevant changes to 5.4 kernel because the issue > definitely exists in 5.4 kernel. > > Thanks, > -- Imran
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