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SubjectRe: Problem with VMAP_STACK=y
On Tue, 4 Oct 2016, Jörg Otte wrote:

> With kernel 4.8.0-01558-g21f54dd I get thousands of
> "dvb-usb: bulk message failed: -11 (1/0)"
> messages in the logs and the DVB adapter is not working.
>
> It tourned out the new config option VMAP_STACK=y (which is the default)
> is the culprit.
> No problems for me with VMAP_STACK=n.

I'd guess that this is EAGAIN coming from usb_hcd_map_urb_for_dma() as the
DVB driver is trying to perform on-stack DMA.

Not really knowing which driver exactly you're using, I quickly skimmed
through DVB sources, and it turns out this indeed seems to be rather
common antipattern, and it should be fixed nevertheless. See

cxusb_ctrl_msg()
dibusb_power_ctrl()
dibusb2_0_streaming_ctrl()
dibusb2_0_power_ctrl()
digitv_ctrl_msg()
dtt200u_fe_init()
dtt200u_fe_set_frontend()
dtt200u_power_ctrl()
dtt200u_streaming_ctrl()
dtt200u_pid_filter()

Adding relevant CCs.

--
Jiri Kosina
SUSE Labs

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