On 12.06.2022 21:28:06, David Laight wrote: > From: Rhett Aultman > > Sent: 10 June 2022 22:34 > > > > The gs_usb driver allocates DMA memory with usb_alloc_coherent() in > > gs_can_open() and then keeps this memory in an URB, with the expectation > > that the memory will be freed when the URB is killed in gs_can_close(). > > Memory allocated with usb_alloc_coherent() cannot be freed in this way > > and must be freed using usb_free_coherent() instead. This means that > > repeated cycles of calling gs_can_open() and gs_can_close() will lead to > > a memory leak. > > > > Historically, drivers have handled this by keeping an array of pointers > > to their DMA rx buffers and explicitly freeing them. For an example of > > this technique used in the esd_usb2 driver, see here: > > https://www.spinics.net/lists/linux-can/msg08203.html > > > > While the above method works, the conditions that cause this leak are > > not apparent to driver writers and the method for solving it at the > > driver level has been piecemeal. This patch makes use of a new > > URB_FREE_COHERENT flag on the URB, reducing the solution of this memory > > leak down to a single line of code. > > > > Signed-off-by: Rhett Aultman <rhett.aultman@xxxxxxxxxxx> > > Reviewed-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> > > --- > > drivers/net/can/usb/gs_usb.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c > > index b29ba9138866..4e7e6a7b961a 100644 > > --- a/drivers/net/can/usb/gs_usb.c > > +++ b/drivers/net/can/usb/gs_usb.c > > @@ -768,7 +768,7 @@ static int gs_can_open(struct net_device *netdev) > > buf, > > dev->parent->hf_size_rx, > > gs_usb_receive_bulk_callback, parent); > > - urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP; > > + urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP | URB_FREE_COHERENT; > > Should that be clearing any other flags? This chance is intentional, Vincent suggested that in | https://lore.kernel.org/all/CAMZ6RqKwvSswxThiKqEB8VhD5MyHvRbSwO_9-ZNwLgmnm-0iBw@xxxxxxxxxxxxxx I think there are no other flags set, yet. regards, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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