Hi Christoph, Ming and others,
On 2/18/25 4:56 PM, Nilay Shroff wrote:
>
>
> On 2/18/25 2:16 PM, Christoph Hellwig wrote:
>> On Tue, Feb 18, 2025 at 01:58:54PM +0530, Nilay Shroff wrote:
>>> There're few sysfs attributes in block layer which don't really need
>>> acquiring q->sysfs_lock while accessing it. The reason being, writing
>>> a value to such attributes are either atomic or could be easily
>>> protected using WRITE_ONCE()/READ_ONCE(). Moreover, sysfs attributes
>>> are inherently protected with sysfs/kernfs internal locking.
>>>
>>> So this change help segregate all existing sysfs attributes for which
>>> we could avoid acquiring q->sysfs_lock. We group all such attributes,
>>> which don't require any sorts of locking, using macro QUEUE_RO_ENTRY_
>>> NOLOCK() or QUEUE_RW_ENTRY_NOLOCK(). The newly introduced show/store
>>> method (show_nolock/store_nolock) is assigned to attributes using these
>>> new macros. The show_nolock/store_nolock run without holding q->sysfs_
>>> lock.
>>
>> Can you add the analys why they don't need sysfs_lock to this commit
>> message please?
> Sure will do it in next patchset.
>>
>> With that:
>>
>> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>>
>
I think we discussed about all attributes which don't require locking,
however there's one which I was looking at "nr_zones" which we haven't
discussed. This is read-only attribute and currently protected with
q->sysfs_lock.
Write to this attribute (nr_zones) mostly happens in the driver probe
method (except nvme) before disk is added and outside of q->sysfs_lock
or any other lock. But in case of nvme it could be updated from disk
scan.
nvme_validate_ns
-> nvme_update_ns_info_block
-> blk_revalidate_disk_zones
-> disk_update_zone_resources
The update to disk->nr_zones is done outside of queue freeze or any
other lock today. So do you agree if we could use READ_ONCE/WRITE_ONCE
to protect this attribute and remove q->sysfs_lock? I think, it'd be
great if we could agree upon this one before I send the next patchset.
Thanks,
--Nilay
