Re: [PATCH v2 0/6] kernfs: proposed locking and concurrency improvement

[Tejun Heo]

Hello,

On Thu, Dec 17, 2020 at 07:48:49PM +0800, Ian Kent wrote:
> > What could be done is to make the kernfs node attr_mutex
> > a pointer and dynamically allocate it but even that is too
> > costly a size addition to the kernfs node structure as
> > Tejun has said.
> 
> I guess the question to ask is, is there really a need to
> call kernfs_refresh_inode() from functions that are usually
> reading/checking functions.
> 
> Would it be sufficient to refresh the inode in the write/set
> operations in (if there's any) places where things like
> setattr_copy() is not already called?
> 
> Perhaps GKH or Tejun could comment on this?

My memory is a bit hazy but invalidations on reads is how sysfs namespace is
implemented, so I don't think there's an easy around that. The only thing I
can think of is embedding the lock into attrs and doing xchg dance when
attaching it.

Thanks.

-- 
tejun