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> > > > > > - curr = xa_cmpxchg(&viommu->vdevs, virt_id, NULL, vdev, GFP_KERNEL); > > > - if (curr) { > > > - rc = xa_err(curr) ?: -EEXIST; > > > + /* > > > + * Reserve the slot with a zero entry (reads back as NULL) until the > > > + * vdevice_init() op accepts the vDEVICE. Only the xa_* helpers hide a > > > + * reserved entry, so never use a raw xas_* iterator on this xarray. > > > + */ > > > + rc = xa_insert(&viommu->vdevs, virt_id, NULL, GFP_KERNEL); > > > + if (rc) { > > > > Why xa_insert() not xa_reserve() ? > > xa_reserve's kdoc says: > "* If there is already something stored at @index, this function does > * nothing" > > By its implementation, it wouldn't return an error on duplication? Yes, OK that's a good reason The way I usually write this pattern is two cmpxchgs, the first NULL -> XA_ZERO_ENTRY and the second XA_ZERO_ENTRY to the final value. The latter failing would be a WARN_ON condition, but this is fine too Jason