On 2/6/26 5:28 PM, Frederic Weisbecker wrote:
Le Fri, Feb 06, 2026 at 03:37:10PM -0500, Waiman Long a écrit :
The update_isolation_cpumasks() function can be called either directly
from regular cpuset control file write with cpuset_full_lock() called
or via the CPU hotplug path with cpus_write_lock and cpuset_mutex held.
As we are going to enable dynamic update to the nozh_full housekeeping
cpumask (HK_TYPE_KERNEL_NOISE) soon with the help of CPU hotplug,
allowing the CPU hotplug path to call into housekeeping_update() directly
from update_isolation_cpumasks() will likely cause deadlock. So we
Why do we need to call housekeeping_update() from hotplug? I would
expect it to be called only when cpuset control file are written since
housekeeping cpumask don't deal with online CPUs but with possible
CPUs.
It needs to call housekeeping_update() only in the special case where
there is only one active CPU in an isolated partition and that CPU goes
offline. In this case, the partition becomes disabled that causes change
in the isolated CPUs. I know this special case shouldn't happen in real
world, but I do have test case to test that.
Theoretically, we can add code to handle this special case to keep this
offline isolated CPU in a special pool without changing isolated_cpus
and hence HK_TYPE_DOMAIN cpumask. In this way, we shouldn't need to
call housekeeping_update() from CPU hotplug. I will probably do that as
CPU hotplug will be used when we make HK_TYPE_KERNEL_NOISE cpumask
dynamic in the near future.
Cheers,
Longman
