Hi,
Wesley Cheng <wcheng@xxxxxxxxxxxxxx> writes:
> The list_for_each_entry_safe() macro saves the current item (n) and
> the item after (n+1), so that n can be safely removed without
> corrupting the list. However, when traversing the list and removing
> items using gadget giveback, the DWC3 lock is briefly released,
> allowing other routines to execute. There is a situation where, while
> items are being removed from the cancelled_list using
> dwc3_gadget_ep_cleanup_cancelled_requests(), the pullup disable
> routine is running in parallel (due to UDC unbind). As the cleanup
> routine removes n, and the pullup disable removes n+1, once the
> cleanup retakes the DWC3 lock, it references a request who was already
> removed/handled. With list debug enabled, this leads to a panic.
> Ensure all instances of the macro are replaced where gadget giveback
> is used.
>
> Example call stack:
>
> Thread#1:
> __dwc3_gadget_ep_set_halt() - CLEAR HALT
> -> dwc3_gadget_ep_cleanup_cancelled_requests()
> ->list_for_each_entry_safe()
> ->dwc3_gadget_giveback(n)
> ->dwc3_gadget_del_and_unmap_request()- n deleted[cancelled_list]
> ->spin_unlock
> ->Thread#2 executes
> ...
> ->dwc3_gadget_giveback(n+1)
> ->Already removed!
>
> Thread#2:
> dwc3_gadget_pullup()
> ->waiting for dwc3 spin_lock
> ...
> ->Thread#1 released lock
> ->dwc3_stop_active_transfers()
> ->dwc3_remove_requests()
> ->fetches n+1 item from cancelled_list (n removed by Thread#1)
> ->dwc3_gadget_giveback()
> ->dwc3_gadget_del_and_unmap_request()- n+1
> deleted[cancelled_list]
> ->spin_unlock
>
> Fix this condition by utilizing list_replace_init(), and traversing
> through a local copy of the current elements in the endpoint lists.
> This will also set the parent list as empty, so if another thread is
> also looping through the list, it will be empty on the next iteration.
>
> Fixes: d4f1afe5e896 ("usb: dwc3: gadget: move requests to cancelled_list")
> Signed-off-by: Wesley Cheng <wcheng@xxxxxxxxxxxxxx>
>
> ---
> Previous patchset:
> https://lore.kernel.org/linux-usb/1620716636-12422-1-git-send-email-wcheng@xxxxxxxxxxxxxx/
> ---
> drivers/usb/dwc3/gadget.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index a29a4ca..3ce6ed9 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -1926,9 +1926,13 @@ static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
> {
> struct dwc3_request *req;
> struct dwc3_request *tmp;
> + struct list_head local;
> struct dwc3 *dwc = dep->dwc;
>
> - list_for_each_entry_safe(req, tmp, &dep->cancelled_list, list) {
> +restart:
> + list_replace_init(&dep->cancelled_list, &local);
hmm, if the lock is held and IRQs disabled when this runs, then no other
threads will be able to append requests to the list which makes the
"restart" label unnecessary, no?
I wonder if we should release the lock and reenable interrupts after
replacing the head. The problem is that
dwc3_gadget_ep_cleanup_cancelled_requests() can run from the IRQ
handler.
Alan, could you provide your insight here? Do you think we should defer
this to a low priority tasklet or something along those lines?
> + list_for_each_entry_safe(req, tmp, &local, list) {
> dwc3_gadget_ep_skip_trbs(dep, req);
> switch (req->status) {
> case DWC3_REQUEST_STATUS_DISCONNECTED:
--
balbi
