iommu: Clear the freelist after iommu_put_pages_list()

The commit below reworked how iommu_put_pages_list() worked to not do
list_del() on every entry. This was done expecting all the callers to
already re-init the list so doing a per-item deletion is not
efficient.

It was missed that fq_ring_free_locked() re-uses its list after calling
iommu_put_pages_list() and so the leftover list reaches free'd struct
pages and will crash or WARN/BUG/etc.

Reinit the list to empty in fq_ring_free_locked() after calling
iommu_put_pages_list().

Audit to see if any other callers of iommu_put_pages_list() need the list
to be empty:

 - iommu_dma_free_fq_single() and iommu_dma_free_fq_percpu() immediately
   frees the memory

 - iommu_v1_map_pages(), v1_free_pgtable(), domain_exit(),
   riscv_iommu_map_pages() uses a stack variable which goes out of scope

 - intel_iommu_tlb_sync() uses a gather in a iotlb_sync() callback, the
   caller re-inits the gather

Fixes: 13f43d7 ("iommu/pages: Formalize the freelist API")
Reported-by: Borah, Chaitanya Kumar <chaitanya.kumar.borah@intel.com>
Closes: https://lore.kernel.org/r/SJ1PR11MB61292CE72D7BE06B8810021CB997A@SJ1PR11MB6129.namprd11.prod.outlook.com
Tested-by: Borah, Chaitanya Kumar <chaitanya.kumar.borah@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/0-v1-7d4dfa6140f7+11f04-iommu_freelist_init_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: jgunthorpe

drivers/iommu/dma-iommu.c

@@ -154,6 +154,8 @@ static void fq_ring_free_locked(struct iommu_dma_cookie *cookie, struct iova_fq
 			       fq->entries[idx].iova_pfn,
 			       fq->entries[idx].pages);
 
+		fq->entries[idx].freelist =
+			IOMMU_PAGES_LIST_INIT(fq->entries[idx].freelist);
 		fq->head = (fq->head + 1) & fq->mod_mask;
 	}
 }

drivers/iommu/iommu-pages.c

@@ -105,7 +105,9 @@ EXPORT_SYMBOL_GPL(iommu_free_pages);
  * iommu_put_pages_list - free a list of pages.
  * @list: The list of pages to be freed
  *
- * Frees a list of pages allocated by iommu_alloc_pages_node_sz().
+ * Frees a list of pages allocated by iommu_alloc_pages_node_sz(). On return the
+ * passed list is invalid, the caller must use IOMMU_PAGES_LIST_INIT to reinit
+ * the list if it expects to use it again.
  */
 void iommu_put_pages_list(struct iommu_pages_list *list)
 {