Re: [PATCH/RFC] usb: fix renesas_usbhs to not schedule in atomiccontext

From: Felipe Balbi
Date: Sun Feb 05 2012 - 09:54:15 EST


On Fri, Feb 03, 2012 at 04:43:20PM +0100, Guennadi Liakhovetski wrote:
> The current renesas_usbhs driver triggers
> BUG: scheduling while atomic: ksoftirqd/0/3/0x00000102
> with enabled CONFIG_DEBUG_ATOMIC_SLEEP, by submitting DMA transfers from
> an atomic (tasklet) context, which is not supported by the shdma dmaengine
> driver. Fix it by switching to a work. Also simplify some list
> manipulations.

you are doing much more than what you say. Also, instead of using a
workqueue, have you considered using threaded_irqs ?

(I didn't go over the driver again to see if it makes sense to use
threaded_irqs in this case, but doesn't hurt asking)

> Shimoda-san, this is the problem, that you were observing. However, it
> exists with the present version of shdma just as well as with the new one
> - on top of the simple DMA library. I marked it an RFC because (1) I only
> lightly tested it with the gadget device on mackerel with the mass storage
> gadget, and (2) I am somewhat concerned about races. Currently the work
> function runs with no locking and there are no usual cancel_work_sync()
> points in the patch. However, it has also been like this before with the
> tasklet implementation, which is not much better, and it looks like there
> are no asynchronous operations on the same packets like timeouts. Only
> asynchronous events, that I can think about are things like unloading the
> driver or unplugging the cable, but these have been there before too. It
> would become worse on SMP, I think. Comments welcome.
> diff --git a/drivers/usb/renesas_usbhs/fifo.c b/drivers/usb/renesas_usbhs/fifo.c
> index 72339bd..4d739ec 100644
> --- a/drivers/usb/renesas_usbhs/fifo.c
> +++ b/drivers/usb/renesas_usbhs/fifo.c
> @@ -75,8 +75,7 @@ void usbhs_pkt_push(struct usbhs_pipe *pipe, struct usbhs_pkt *pkt,
> pipe->handler = &usbhsf_null_handler;
> }
> - list_del_init(&pkt->node);
> - list_add_tail(&pkt->node, &pipe->list);
> + list_move_tail(&pkt->node, &pipe->list);
> /*
> * each pkt must hold own handler.
> @@ -106,7 +105,7 @@ static struct usbhs_pkt *__usbhsf_pkt_get(struct usbhs_pipe *pipe)
> if (list_empty(&pipe->list))
> return NULL;
> - return list_entry(pipe->, struct usbhs_pkt, node);
> + return list_first_entry(&pipe->list, struct usbhs_pkt, node);

these two hunks are not part of $SUBJECT


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