Re: [PATCH v3] block: Remove queue freezing from several sysfs store callbacks

[Nilay Shroff <nilay@linux.ibm.com>]

On 11/3/25 9:42 AM, Ming Lei wrote:
> On Fri, Oct 31, 2025 at 8:40 PM Nilay Shroff <nilay@linux.ibm.com> wrote:
>>
>>
>>
>> On 10/30/25 10:54 PM, Bart Van Assche wrote:
>>> Fix this by removing the blk_mq_freeze_queue() / blk_mq_unfreeze_queue()
>>> calls from the store callbacks that do not strictly need these callbacks.
>>> This patch may cause a small delay in applying the new settings.
>>>
>>> This patch affects the following sysfs attributes:
>>> * io_poll_delay
>>> * io_timeout
>>> * nomerges
>>> * read_ahead_kb
>>> * rq_affinity
>>
>> I see that io_timeout, nomerges and rq_affinity are all accessed
>> during I/O hotpath. So IMO for these attributes we still need to
>> freeze the queue before updating those parameters. The io_timeout
>> and nomerges are accessed during I/O submission and rq_affinity
>> is accessed during I/O completion.
> 
> Does freeze make any difference? Intermediate value isn't possible, and
> either the old or new value should be just fine to take.
> 
Yes it doesn't affect the I/O and so if we remove freeze/unfreeze 
calls for these attributes then we may still need to annotate 
it with data_race and/or READ_ONCE as Christoph mentioned in another 
thread. I saw that nomerges and rq_affinity already uses atomic
bitmap and so we may still need to annotate io_timeout.

Thanks,
--Nilay