Hi, "Felipe F. Tonello" <e...@felipetonello.com> 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: <sta...@vger.kernel.org> # 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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