dma: at_xdmac: fix a missing check on list iterator

stable inclusion
from stable-v5.10.113
commit 358a3846f6a950b8db803262e74081ad4ab235d4
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ISAH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=358a3846f6a950b8db803262e74081ad4ab235d4

--------------------------------

commit 206680c upstream.

The bug is here:
	__func__, desc, &desc->tx_dma_desc.phys, ret, cookie, residue);

The list iterator 'desc' will point to a bogus position containing
HEAD if the list is empty or no element is found. To avoid dev_dbg()
prints a invalid address, use a new variable 'iter' as the list
iterator, while use the origin variable 'desc' as a dedicated
pointer to point to the found element.

Cc: [email protected]
Fixes: 82e2424 ("dmaengine: xdmac: fix print warning on dma_addr_t variable")
Signed-off-by: Xiaomeng Tong <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Zheng Zengkai <[email protected]>
Acked-by: Xie XiuQi <[email protected]>

drivers/dma/at_xdmac.c

@@ -1390,7 +1390,7 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
 {
 	struct at_xdmac_chan	*atchan = to_at_xdmac_chan(chan);
 	struct at_xdmac		*atxdmac = to_at_xdmac(atchan->chan.device);
-	struct at_xdmac_desc	*desc, *_desc;
+	struct at_xdmac_desc	*desc, *_desc, *iter;
 	struct list_head	*descs_list;
 	enum dma_status		ret;
 	int			residue, retry;
@@ -1505,11 +1505,13 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
 	 * microblock.
 	 */
 	descs_list = &desc->descs_list;
-	list_for_each_entry_safe(desc, _desc, descs_list, desc_node) {
-		dwidth = at_xdmac_get_dwidth(desc->lld.mbr_cfg);
-		residue -= (desc->lld.mbr_ubc & 0xffffff) << dwidth;
-		if ((desc->lld.mbr_nda & 0xfffffffc) == cur_nda)
+	list_for_each_entry_safe(iter, _desc, descs_list, desc_node) {
+		dwidth = at_xdmac_get_dwidth(iter->lld.mbr_cfg);
+		residue -= (iter->lld.mbr_ubc & 0xffffff) << dwidth;
+		if ((iter->lld.mbr_nda & 0xfffffffc) == cur_nda) {
+			desc = iter;
 			break;
+		}
 	}
 	residue += cur_ubc << dwidth;