On 12/31/25 7:02 AM, Frederic Weisbecker wrote:
> Le Mon, Dec 29, 2025 at 05:37:29PM -0700, Jens Axboe a ?crit :
>> On 12/24/25 6:44 AM, Frederic Weisbecker wrote:
>>> The block subsystem prevents running the workqueue to isolated CPUs,
>>> including those defined by cpuset isolated partitions. Since
>>> HK_TYPE_DOMAIN will soon contain both and be subject to runtime
>>> modifications, synchronize against housekeeping using the relevant lock.
>>>
>>> For full support of cpuset changes, the block subsystem may need to
>>> propagate changes to isolated cpumask through the workqueue in the
>>> future.
>>>
>>> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
>>> ---
>>> block/blk-mq.c | 6 +++++-
>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>>> index 1978eef95dca..0037af1216f3 100644
>>> --- a/block/blk-mq.c
>>> +++ b/block/blk-mq.c
>>> @@ -4257,12 +4257,16 @@ static void blk_mq_map_swqueue(struct request_queue *q)
>>>
>>> /*
>>> * Rule out isolated CPUs from hctx->cpumask to avoid
>>> - * running block kworker on isolated CPUs
>>> + * running block kworker on isolated CPUs.
>>> + * FIXME: cpuset should propagate further changes to isolated CPUs
>>> + * here.
>>> */
>>> + rcu_read_lock();
>>> for_each_cpu(cpu, hctx->cpumask) {
>>> if (cpu_is_isolated(cpu))
>>> cpumask_clear_cpu(cpu, hctx->cpumask);
>>> }
>>> + rcu_read_unlock();
>>
>> Want me to just take this one separately and get it out of your hair?
>> Doesn't seem to have any dependencies.
>
> The patch could be applied alone but the rest of the patchset needs it,
> otherwise it may dereference freed memory. So I fear it needs to stay
> within the lot.
>
> I appreciate the offer though. But an ack would help, even if I must admit
> this single patch (which doesn't change current behaviour) leaves a
> bitter taste because complete handling of cpuset isolated partition change
> will require more work.
That's fine too:
Acked-by: Jens Axboe <axboe@kernel.dk>
> Speaking of, is there a way that I missed to define/overwrite the above
> hctx->cpumask on runtime?
Only spot where it's set/manipulated right now is as part of setting up
the hctx <-> ctx queue mappings, when the queue is configured (or
reconfigured).
--
Jens Axboe