Re: [PATCHv2 1/6] blk-sysfs: remove q->sysfs_lock for attributes which don't need it

[Ming Lei <ming.lei@redhat.com>]

On Tue, Feb 18, 2025 at 05:29:53PM +0100, Christoph Hellwig wrote:
> On Tue, Feb 18, 2025 at 09:45:02PM +0800, Ming Lei wrote:
> > IMO, this RO attributes needn't protection from q->limits_lock:
> > 
> > - no lifetime issue
> > 
> > - in-tree code needn't limits_lock.
> > 
> > - all are scalar variable, so the attribute itself is updated atomically
> 
> Except in the memory model they aren't without READ_ONCE/WRITE_ONCE.

RW_ONCE is supposed for avoiding compiler optimization, and scalar
variable atomic update should be decided by hardware.

> 
> Given that the limits_lock is not a hot lock taking the lock is a very
> easy way to mark our intent.  And if we get things like thread thread
> sanitizer patches merged that will become essential.  Even KCSAN
> might object already without it.

My main concern is that there are too many ->store()/->load() variants
now, but not deal if you think this way is fine, :-)

Thanks,
Ming