On Thu, Jan 03, 2019 at 10:30:26PM +0000, Jason Gunthorpe wrote:
> On Thu, Jan 03, 2019 at 10:05:59AM +0200, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@xxxxxxxxxxxx>
> >
> > XArray uses internal lock for updates to XArray. This means that our
> > external RW lock is not needed anymore and we can delete it.
>
> The xarray lock only protects the array itself - not the things it
> points to.
>
> > - down_read(&res->rwsem);
> > xa_for_each(&res->xa[type], e, index, ULONG_MAX, XA_PRESENT) {
> > if (ns == &init_pid_ns ||
> > (!rdma_is_kernel_res(e) &&
>
> So eg here, 'e' is still needs the locking to protect against
> concurrent restrack_del causing e to be freed.
>
> Most likely the internal xarray locking doesn't save anything in this
> usage..
The "rwsem" protects hash lists insert/delete and we are still using
kref to protect specific entries. And those xarray insert/deletion are
handled by xa_lock() now.
>
> Jason
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