On 2/19/26 5:02 PM, Koralahalli Channabasappa, Smita wrote:
> Hi Dave,
>
> On 2/18/2026 9:52 AM, Dave Jiang wrote:
>>
>>
>> On 2/9/26 11:44 PM, Smita Koralahalli wrote:
>>> Add helpers to register, queue and flush the deferred work.
>>>
>>> These helpers allow dax_hmem to execute ownership resolution outside the
>>> probe context before dax_cxl binds.
>>>
>>> Signed-off-by: Smita Koralahalli <[email protected]>
>>> ---
>>> drivers/dax/bus.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++
>>> drivers/dax/bus.h | 7 ++++++
>>> 2 files changed, 65 insertions(+)
>>>
>>> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
>>> index 5f387feb95f0..92b88952ede1 100644
>>> --- a/drivers/dax/bus.c
>>> +++ b/drivers/dax/bus.c
>>> @@ -25,6 +25,64 @@ DECLARE_RWSEM(dax_region_rwsem);
>>> */
>>> DECLARE_RWSEM(dax_dev_rwsem);
>>> +static DEFINE_MUTEX(dax_hmem_lock);
>>> +static dax_hmem_deferred_fn hmem_deferred_fn;
>>> +static void *dax_hmem_data;
>>> +
>>> +static void hmem_deferred_work(struct work_struct *work)
>>> +{
>>> + dax_hmem_deferred_fn fn;
>>> + void *data;
>>> +
>>> + scoped_guard(mutex, &dax_hmem_lock) {
>>> + fn = hmem_deferred_fn;
>>> + data = dax_hmem_data;
>>> + }
>>> +
>>> + if (fn)
>>> + fn(data);
>>> +}
>>
>> Instead of having a global lock and dealing with all the global variables,
>> why not just do this with the typical work_struct usage pattern and allocate
>> a work item when queuing work?
>>
>> DJ
>
> Thanks for the feedback.
>
> Just to clarify, are you hinting towards a statically allocated struct
> with an embedded work_struct, something like below? Rather than the typical
> kmalloc + container_of pattern?
>
> +struct dax_hmem_deferred_ctx {
> + struct work_struct work;
> + dax_hmem_deferred_fn fn;
> + void *data;
> +};
>
> +static struct dax_hmem_deferred_ctx dax_hmem_ctx;
>
> +int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data)
> +{
> + if (dax_hmem_ctx.fn)
> + return -EINVAL;
>
> + INIT_WORK(&dax_hmem_ctx.work, hmem_deferred_work);
> ..
>
> My understanding is that Dan wanted this to remain a singleton deferred work
> item queued once and flushed from dax_cxl. I think with kmalloc +
> container_of approach, every call would allocate and queue a new independent
> work item..
>
> Regarding the mutex: looking at it again, it may not be necessary I think. If
> we can rely on the call ordering (register_work() before queue_work()), and
> if flush_work() in kill_defer_work() ensures the work has fully completed
> before unregister_work() NULLs the pointers, then the static struct above
> would be sufficient without additional locking. If I'm missing a scenario or
> race here, please correct me.
Ok I missed the history on the single issue work item. Yes what you proposed
above should work if it's single issue. and if we are only sending 1 item, a
statically declared work context should be sufficient I think.
DJ
>
> Thanks,
> Smita
>
>>
>>> +
>>> +static DECLARE_WORK(dax_hmem_work, hmem_deferred_work);
>>> +
>>> +int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data)
>>> +{
>>> + guard(mutex)(&dax_hmem_lock);
>>> +
>>> + if (hmem_deferred_fn)
>>> + return -EINVAL;
>>> +
>>> + hmem_deferred_fn = fn;
>>> + dax_hmem_data = data;
>>> + return 0;
>>> +}
>>> +EXPORT_SYMBOL_GPL(dax_hmem_register_work);
>>> +
>>> +int dax_hmem_unregister_work(dax_hmem_deferred_fn fn, void *data)
>>> +{
>>> + guard(mutex)(&dax_hmem_lock);
>>> +
>>> + if (hmem_deferred_fn != fn || dax_hmem_data != data)
>>> + return -EINVAL;
>>> +
>>> + hmem_deferred_fn = NULL;
>>> + dax_hmem_data = NULL;
>>> + return 0;
>>> +}
>>> +EXPORT_SYMBOL_GPL(dax_hmem_unregister_work);
>>> +
>>> +void dax_hmem_queue_work(void)
>>> +{
>>> + queue_work(system_long_wq, &dax_hmem_work);
>>> +}
>>> +EXPORT_SYMBOL_GPL(dax_hmem_queue_work);
>>> +
>>> +void dax_hmem_flush_work(void)
>>> +{
>>> + flush_work(&dax_hmem_work);
>>> +}
>>> +EXPORT_SYMBOL_GPL(dax_hmem_flush_work);
>>> +
>>> #define DAX_NAME_LEN 30
>>> struct dax_id {
>>> struct list_head list;
>>> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
>>> index cbbf64443098..b58a88e8089c 100644
>>> --- a/drivers/dax/bus.h
>>> +++ b/drivers/dax/bus.h
>>> @@ -41,6 +41,13 @@ struct dax_device_driver {
>>> void (*remove)(struct dev_dax *dev);
>>> };
>>> +typedef void (*dax_hmem_deferred_fn)(void *data);
>>> +
>>> +int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data);
>>> +int dax_hmem_unregister_work(dax_hmem_deferred_fn fn, void *data);
>>> +void dax_hmem_queue_work(void);
>>> +void dax_hmem_flush_work(void);
>>> +
>>> int __dax_driver_register(struct dax_device_driver *dax_drv,
>>> struct module *module, const char *mod_name);
>>> #define dax_driver_register(driver) \
>>
>
