Re: [PATCH 04/10] staging: erofs: fix `erofs_workgroup_{try_to_freeze, unfreeze}'

[Greg Kroah-Hartman]

On Thu, Nov 22, 2018 at 06:29:34PM +0800, Gao Xiang wrote:
> Hi Greg,
> 
> On 2018/11/22 18:21, Greg Kroah-Hartman wrote:
> > On Tue, Nov 20, 2018 at 10:34:19PM +0800, Gao Xiang wrote:
> >> There are two minor issues in the current freeze interface:
> >>
> >>    1) Freeze interfaces have not related with CONFIG_DEBUG_SPINLOCK,
> >>       therefore fix the incorrect conditions;
> >>
> >>    2) For SMP platforms, it should also disable preemption before
> >>       doing atomic_cmpxchg in case that some high priority tasks
> >>       preempt between atomic_cmpxchg and disable_preempt, then spin
> >>       on the locked refcount later.
> > 
> > spinning on a refcount implies that you are trying to do your own type
> > of locking.  Why not use the in-kernel locking api instead?  It will
> > always do better than trying to do your own logic as the developers
> > there know locking across all types of cpus better than filesystem
> > developers :)
> 
> It is because refcount also plays a role as a spinlock on a specific value
> (== EROFS_LOCKED_MAGIC), no need to introduce such a value since the spin
> window is small.

As I said in another email, doing two things with one variable is odd as
those are two different types of functions.

greg k-h