On Wed, Nov 04, 2020 at 02:58:43PM -0400, Jason Gunthorpe wrote:
> > static void cm_finalize_id(struct cm_id_private *cm_id_priv)
> > {
> > xa_store_irq(&cm.local_id_table, cm_local_id(cm_id_priv->id.local_id),
> > - cm_id_priv, GFP_KERNEL);
> > + cm_id_priv);
> > }
>
> This one is almost a bug, the entry is preallocated with NULL though:
>
> ret = xa_alloc_cyclic_irq(&cm.local_id_table, &id, NULL, xa_limit_32b,
> &cm.local_id_next, GFP_KERNEL);
>
> so it should never allocate here:
>
> static int cm_req_handler(struct cm_work *work)
> {
> spin_lock_irq(&cm_id_priv->lock);
> cm_finalize_id(cm_id_priv);
Uhm. I think you want a different debugging check from this. The actual
bug here is that you'll get back from calling cm_finalize_id() with
interrupts enabled. Can you switch to xa_store(), or do we need an
xa_store_irqsave()?
> Still, woops.
>
> Matt, maybe a might_sleep is deserved in here someplace?
>
> @@ -1534,6 +1534,8 @@ void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
> XA_STATE(xas, xa, index);
> void *curr;
>
> + might_sleep_if(gfpflags_allow_blocking(gfp));
> +
> if (WARN_ON_ONCE(xa_is_advanced(entry)))
> return XA_ERROR(-EINVAL);
> if (xa_track_free(xa) && !entry)
>
> And similar in the other places that conditionally call __xas_nomem()
> ?
>
> I also still wish there was a proper 'xa store in already allocated
> but null' idiom - I remember you thought about using gfp flags == 0 at
> one point.
An xa_replace(), perhaps?
