linux-kernel - Re: Problem with VMAP

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Date:   Tue, 4 Oct 2016 15:26:28 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Jörg Otte <jrg.otte@...il.com>
cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Michael Krufky <mkrufky@...uxtv.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Patrick Boettcher <patrick.boettcher@...teo.de>,
        linux-media@...r.kernel.org
Subject: Re: 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