Re: [PATCH v4 4/6] kernfs: Don't re-lock kernfs_root::kernfs_rwsem in kernfs_fop_readdir().

[Tejun Heo]

On Mon, Jan 27, 2025 at 10:02:00AM +0100, Sebastian Andrzej Siewior wrote:
> On 2025-01-24 13:15:32 [-1000], Tejun Heo wrote:
> > Hello,
> > 
> > On Fri, Jan 24, 2025 at 06:46:12PM +0100, Sebastian Andrzej Siewior wrote:
> > ...
> > > to avoid holding a global lock during a page fault. The lock drop is
> > > wrong since the support of renames and not a big burden since the lock
> > > is no longer global.
> > 
> > It's still a pretty big lock. Hopefully, at least name accesses can be
> > converted to rcu protected ones later?
> 
> Not sure what you mean by "rcu protected ones". The name is already RCU
> protected which is part of the problem :P
> Assuming an upper length of name to be around 255 and
> kernfs_fop_readdir() to be very early on the chain then we could copy
> the name on stack within the RCU section and do this without
> ::kernfs_rwsem.

Please ignore me on this one. I'll take a better look next round.

Thanks.

-- 
tejun