Looks like these patches are the fixes.
https://lore.kernel.org/all/YtDvN0wJ6CKaEPN8@xxxxxxxxxxxxxxx/#r
Would let Tejun confirm this .
-Mukesh
On 7/20/2022 4:36 PM, Mukesh Ojha wrote:
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@xxxxxxxxxx/
-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
