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Subject[PATCH v3] usb: dwc3: gadget: Move null pinter check after window closed
From
After inspecting further, we do see the locking is implicit, with the
main gotcha being the unlock/re-lock. That creates a window for a race
to happen. This change moves the NULL check to be adjacent to where
to it's used and after the window is "closed".

Fixes: 26288448120b ("usb: dwc3: gadget: Fix null pointer exception")
Signed-off-by: Albert Wang <albertccwang@google.com>
---
v3: Add change log to be compliant with the canonical patch format
v2: Remove redundant 'else' and add additional comments and more
descriptive commit text

drivers/usb/dwc3/gadget.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 19477f4bbf54..fda58951cf27 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -3366,14 +3366,19 @@ static bool dwc3_gadget_endpoint_trbs_complete(struct dwc3_ep *dep,
struct dwc3 *dwc = dep->dwc;
bool no_started_trb = true;

- if (!dep->endpoint.desc)
- return no_started_trb;
-
+ /*
+ * This function eventually leads to dwc3_giveback() which unlocks
+ * the dwc->lock and relocks afterwards. This actually creates a
+ * a window for a race to happen.
+ */
dwc3_gadget_ep_cleanup_completed_requests(dep, event, status);

if (dep->flags & DWC3_EP_END_TRANSFER_PENDING)
goto out;

+ if (!dep->endpoint.desc)
+ return no_started_trb;
+
if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
list_empty(&dep->started_list) &&
(list_empty(&dep->pending_list) || status == -EXDEV))
--
2.36.0.550.gb090851708-goog
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