Re: [PATCH v3] cgroup/cpuset-v1: Add missing support for cpuset_v2_mode

[Tejun Heo <tj@kernel.org>]

On Wed, Apr 16, 2025 at 09:17:51PM +0000, T.J. Mercier wrote:
> Android has mounted the v1 cpuset controller using filesystem type
> "cpuset" (not "cgroup") since 2015 [1], and depends on the resulting
> behavior where the controller name is not added as a prefix for cgroupfs
> files. [2]
> 
> Later, a problem was discovered where cpu hotplug onlining did not
> affect the cpuset/cpus files, which Android carried an out-of-tree patch
> to address for a while. An attempt was made to upstream this patch, but
> the recommendation was to use the "cpuset_v2_mode" mount option
> instead. [3]
> 
> An effort was made to do so, but this fails with "cgroup: Unknown
> parameter 'cpuset_v2_mode'" because commit e1cba4b85daa ("cgroup: Add
> mount flag to enable cpuset to use v2 behavior in v1 cgroup") did not
> update the special cased cpuset_mount(), and only the cgroup (v1)
> filesystem type was updated.
> 
> Add parameter parsing to the cpuset filesystem type so that
> cpuset_v2_mode works like the cgroup filesystem type:
> 
> $ mkdir /dev/cpuset
> $ mount -t cpuset -ocpuset_v2_mode none /dev/cpuset
> $ mount|grep cpuset
> none on /dev/cpuset type cgroup (rw,relatime,cpuset,noprefix,cpuset_v2_mode,release_agent=/sbin/cpuset_release_agent)
> 
> [1] https://cs.android.com/android/_/android/platform/system/core/+/b769c8d24fd7be96f8968aa4c80b669525b930d3
> [2] https://cs.android.com/android/platform/superproject/main/+/main:system/core/libprocessgroup/setup/cgroup_map_write.cpp;drc=2dac5d89a0f024a2d0cc46a80ba4ee13472f1681;l=192
> [3] https://lore.kernel.org/lkml/f795f8be-a184-408a-0b5a-553d26061385@redhat.com/T/
> 
> Fixes: e1cba4b85daa ("cgroup: Add mount flag to enable cpuset to use v2 behavior in v1 cgroup")
> Signed-off-by: T.J. Mercier <tjmercier@google.com>
> Acked-by: Waiman Long <longman@redhat.com>
> Reviewed-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
> Acked-by: Michal Koutný <mkoutny@suse.com>

Applied to cgroup/for-6.15-fixes.

Thanks.

-- 
tejun