[PATCH 6.18 343/752] usb: chipidea: udc: fix DMA and SG cleanup in _ep_nuke()

Sasha Levin
2026-02-28T17:52:55Z

From: Mario Peter <mario.peter@leica-geosystems.com>

[ Upstream commit cea2a1257a3b5ea3e769a445b34af13e6aa5a123 ]

The ChipIdea UDC driver can encounter "not page aligned sg buffer"
errors when a USB device is reconnected after being disconnected
during an active transfer. This occurs because _ep_nuke() returns
requests to the gadget layer without properly unmapping DMA buffers
or cleaning up scatter-gather bounce buffers.

Root cause:
When a disconnect happens during a multi-segment DMA transfer, the
request's num_mapped_sgs field and sgt.sgl pointer remain set with
stale values. The request is returned to the gadget driver with status
-ESHUTDOWN but still has active DMA state. If the gadget driver reuses
this request on reconnect without reinitializing it, the stale DMA
state causes _hardware_enqueue() to skip DMA mapping (seeing non-zero
num_mapped_sgs) and attempt to use freed/invalid DMA addresses,
leading to alignment errors and potential memory corruption.

The normal completion path via _hardware_dequeue() properly calls
usb_gadget_unmap_request_by_dev() and sglist_do_debounce() before
returning the request. The _ep_nuke() path must do the same cleanup
to ensure requests are returned in a clean, reusable state.

Fix:
Add DMA unmapping and bounce buffer cleanup to _ep_nuke() to mirror
the cleanup sequence in _hardware_dequeue():
- Call usb_gadget_unmap_request_by_dev() if num_mapped_sgs is set
- Call sglist_do_debounce() with copy=false if bounce buffer exists

This ensures that when requests are returned due to endpoint shutdown,
they don't retain stale DMA mappings. The 'false' parameter to
sglist_do_debounce() prevents copying data back (appropriate for
shutdown path where transfer was aborted).

Signed-off-by: Mario Peter <mario.peter@leica-geosystems.com>
Reviewed-by: Xu Yang <xu.yang_2@nxp.com>
Acked-by: Peter Chen <peter.chen@kernel.org>
Link: https://patch.msgid.link/20260108165902.795354-1-mario.peter@leica-geosystems.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/usb/chipidea/udc.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c
index 64a421ae0f05b..c8d931d9d4330 100644
--- a/drivers/usb/chipidea/udc.c
+++ b/drivers/usb/chipidea/udc.c
@@ -931,6 +931,13 @@ __acquires(hwep->lock)
list_del_init(&hwreq->queue);
hwreq->req.status = -ESHUTDOWN;

+ /* Unmap DMA and clean up bounce buffers before giving back */
+ usb_gadget_unmap_request_by_dev(hwep->ci->dev->parent,
+ &hwreq->req, hwep->dir);
+
+ if (hwreq->sgt.sgl)
+ sglist_do_debounce(hwreq, false);
+
if (hwreq->req.complete != NULL) {
spin_unlock(hwep->lock);
usb_gadget_giveback_request(&hwep->ep, &hwreq->req);
--
2.51.0