linux-kernel - Re: [PATCH] media: add GFP flag to media_*() that could get called in atomic context

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Date:	Mon, 14 Mar 2016 11:33:25 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	"Mauro Carvalho Chehab" <mchehab@....samsung.com>
Cc:	"Sakari Ailus" <sakari.ailus@....fi>,
	<alsa-devel@...a-project.org>, <hans.verkuil@...co.com>,
	<lixiubo@...s.chinamobile.com>, <devel@...verdev.osuosl.org>,
	<amitoj1606@...il.com>, <chehabrafael@...il.com>,
	<hamohammed.sa@...il.com>, <navyasri.tech@...il.com>,
	<prabhakar.csengg@...il.com>, <g.liakhovetski@....de>,
	<der.herr@...r.at>, <laurent.pinchart@...asonboard.com>,
	<crope@....fi>, <tommi.franttila@...el.com>, <kgene@...nel.org>,
	<gregkh@...uxfoundation.org>, <Julia.Lawall@...6.fr>,
	<linux-arm-kernel@...ts.infradead.org>, <dan.carpenter@...cle.com>,
	<javier@....samsung.com>, "Shuah Khan" <shuahkh@....samsung.com>,
	<perex@...ex.cz>, <a.hajda@...sung.com>, <k.kozlowski@...sung.com>,
	<kyungmin.park@...sung.com>, <s.nawrocki@...sung.com>,
	<linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
	<linux-renesas-soc@...r.kernel.org>,
	<linux-samsung-soc@...r.kernel.org>, <hyun.kwon@...inx.com>,
	<soren.brinkmann@...inx.com>
Subject: Re: [PATCH] media: add GFP flag to media_*() that could get called in atomic context

On Mon, 14 Mar 2016 11:13:58 +0100,
Mauro Carvalho Chehab wrote:
> 
> Em Mon, 14 Mar 2016 09:22:37 +0200
> Sakari Ailus <sakari.ailus@....fi> escreveu:
> 
> > Hi Shuah,
> > 
> > On Sat, Mar 12, 2016 at 06:48:09PM -0700, Shuah Khan wrote:
> > > Add GFP flags to media_create_pad_link(), media_create_intf_link(),
> > > media_devnode_create(), and media_add_link() that could get called
> > > in atomic context to allow callers to pass in the right flags for
> > > memory allocation.
> > > 
> > > tree-wide driver changes for media_*() GFP flags change:
> > > Change drivers to add gfpflags to interffaces, media_create_pad_link(),
> > > media_create_intf_link() and media_devnode_create().
> > > 
> > > Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
> > > Suggested-by: Mauro Carvalho Chehab <mchehab@....samsung.com>  
> > 
> > What's the use case for calling the above functions in an atomic context?
> > 
> 
> ALSA code seems to do a lot of stuff at atomic context. That's what
> happens on my test machine when au0828 gets probed before
> snd-usb-audio:
> 	http://pastebin.com/LEX5LD5K
> 
> It seems that ALSA USB probe routine (usb_audio_probe) happens in
> atomic context.

No, usb_audio_probe() doesn't take a lock.  But
media_device_register_entity() seems taking a spinlock, instead.


Takashi