Hi,
"Felipe F. Tonello" <eu@xxxxxxxxxxxxxxxxx> writes:
> [ text/plain ]
> Since f_midi_transmit is called by both ALSA and USB sub-systems, it can
> potentially cause a race condition between both calls because f_midi_transmit
> is not reentrant nor thread-safe. This is due to an implementation detail that
> the transmit function looks for the next available usb request from the fifo
> and only enqueues it if there is data to send, otherwise just re-uses it. So,
> if both ALSA and USB frameworks calls this function at the same time,
> kfifo_seek() will return the same usb_request, which will cause a race
> condition.
>
> To solve this problem a syncronization mechanism is necessary. In this case it
> is used a spinlock since f_midi_transmit is also called by usb_request->complete
> callback in interrupt context.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.4+
this should be v4.5+
$ git describe e1e3d7ec5da3
v4.4-rc5-59-ge1e3d7ec5da3
> @@ -651,17 +653,22 @@ static void f_midi_transmit(struct f_midi *midi)
> {
> struct usb_ep *ep = midi->in_ep;
> int ret;
> + unsigned long flags;
>
> /* We only care about USB requests if IN endpoint is enabled */
> if (!ep || !ep->enabled)
> goto drop_out;
>
> + spin_lock_irqsave(&midi->transmit_lock, flags);
> +
> do {
> ret = f_midi_do_transmit(midi, ep);
you wrote this commit on top of 'next' right ? I know that because of
this call to f_midi_do_transmit() here which is introduced by commit
aac887442d5e ("usb: gadget: f_midi: move some of f_midi_transmit to
separate func") which is not in Linus' tree yet.
This prevents me from taking this patch during current -rc.
--
balbi
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