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From: Peter Rosin <peda@axentia.se>
To: Philipp Zabel <p.zabel@pengutronix.de>
Cc: linux-media@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org,
	Steve Longerbeam <steve_longerbeam@mentor.com>,
	kernel@pengutronix.de, Sascha Hauer <s.hauer@pengutronix.de>,
	Rob Herring <robh+dt@kernel.org>,
	Sakari Ailus <sakari.ailus@iki.fi>, Pavel Machek <pavel@ucw.cz>,
	Steve Longerbeam <slongerbeam@gmail.com>,
	Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Subject: Re: [PATCH 2/2] [media] platform: add video-multiplexer subdevice driver
Date: Wed, 3 May 2017 13:13:42 +0200	[thread overview]
Message-ID: <e1cda75b-4967-7d79-7f07-b4f392153d73@axentia.se> (raw)
In-Reply-To: <1493800556.3599.15.camel@pengutronix.de>

On 2017-05-03 10:35, Philipp Zabel wrote:
> On Tue, 2017-05-02 at 19:42 +0200, Peter Rosin wrote:
>> On 2017-05-02 17:21, Philipp Zabel wrote:
>>> Thank you, I've resent a version with a mutex lock around vmux->active.
>>
>> I had a bunch of ifs in the above message, so I'm not sure it's needed.
>> I would expect there to be a lock outside somewhere in the media layer.
>> A cursory look gets me to media-entity.c and media_entity_setup_link()
>> which does have a mutex. But I'm no media expert, so maybe there are other
>> ways of getting to video_mux_link_setup that I'm not aware of?
> 
> link_setup is always called under the graph mutex of the /dev/media
> device. That is why I didn't think about locking too hard. In fact, I
> initially wrote this expecting mux_control_get_exclusive to exist and
> the mux select/deselect not to be locked at all.
> 
> But set_format is called from an unlocked ioctl on a /dev/v4l-subdev
> device. Until your comments I didn't notice that it would be possible to
> let link_setup set active = -1 in the middle of the set_format call,
> causing it to return garbage.

Obviously, now that you point it out. I completely missed set_format...

Cheers,
peda

WARNING: multiple messages have this Message-ID (diff)
From: Peter Rosin <peda@axentia.se>
To: Philipp Zabel <p.zabel@pengutronix.de>
Cc: <linux-media@vger.kernel.org>,
	Mark Rutland <mark.rutland@arm.com>, <devicetree@vger.kernel.org>,
	Steve Longerbeam <steve_longerbeam@mentor.com>,
	<kernel@pengutronix.de>, Sascha Hauer <s.hauer@pengutronix.de>,
	Rob Herring <robh+dt@kernel.org>,
	Sakari Ailus <sakari.ailus@iki.fi>, Pavel Machek <pavel@ucw.cz>,
	Steve Longerbeam <slongerbeam@gmail.com>,
	Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Subject: Re: [PATCH 2/2] [media] platform: add video-multiplexer subdevice driver
Date: Wed, 3 May 2017 13:13:42 +0200	[thread overview]
Message-ID: <e1cda75b-4967-7d79-7f07-b4f392153d73@axentia.se> (raw)
In-Reply-To: <1493800556.3599.15.camel@pengutronix.de>

On 2017-05-03 10:35, Philipp Zabel wrote:
> On Tue, 2017-05-02 at 19:42 +0200, Peter Rosin wrote:
>> On 2017-05-02 17:21, Philipp Zabel wrote:
>>> Thank you, I've resent a version with a mutex lock around vmux->active.
>>
>> I had a bunch of ifs in the above message, so I'm not sure it's needed.
>> I would expect there to be a lock outside somewhere in the media layer.
>> A cursory look gets me to media-entity.c and media_entity_setup_link()
>> which does have a mutex. But I'm no media expert, so maybe there are other
>> ways of getting to video_mux_link_setup that I'm not aware of?
> 
> link_setup is always called under the graph mutex of the /dev/media
> device. That is why I didn't think about locking too hard. In fact, I
> initially wrote this expecting mux_control_get_exclusive to exist and
> the mux select/deselect not to be locked at all.
> 
> But set_format is called from an unlocked ioctl on a /dev/v4l-subdev
> device. Until your comments I didn't notice that it would be possible to
> let link_setup set active = -1 in the middle of the set_format call,
> causing it to return garbage.

Obviously, now that you point it out. I completely missed set_format...

Cheers,
peda

  reply	other threads:[~2017-05-03 11:13 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-28 14:13 [PATCH 1/2] [media] dt-bindings: Add bindings for video-multiplexer device Philipp Zabel
2017-04-28 14:13 ` [PATCH 2/2] [media] platform: add video-multiplexer subdevice driver Philipp Zabel
     [not found]   ` <20170428141330.16187-2-p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
2017-04-29 21:29     ` Peter Rosin
2017-04-29 21:29       ` Peter Rosin
     [not found]       ` <beb9f7c4-4959-1bb2-03e2-c5ccecbb8368-koto5C5qi+TLoDKTGw+V6w@public.gmane.org>
2017-04-29 21:42         ` Peter Rosin
2017-04-29 21:42           ` Peter Rosin
     [not found]           ` <df5f38c4-b0e8-64c6-d6ba-c554133f4bbf-koto5C5qi+TLoDKTGw+V6w@public.gmane.org>
2017-05-02 15:21             ` Philipp Zabel
2017-05-02 15:21               ` Philipp Zabel
     [not found]               ` <1493738491.2391.20.camel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
2017-05-02 17:42                 ` Peter Rosin
2017-05-02 17:42                   ` Peter Rosin
     [not found]                   ` <74bfa70b-3407-9484-9717-bb2d07356f70-koto5C5qi+TLoDKTGw+V6w@public.gmane.org>
2017-05-03  8:35                     ` Philipp Zabel
2017-05-03  8:35                       ` Philipp Zabel
2017-05-03 11:13                       ` Peter Rosin [this message]
2017-05-03 11:13                         ` Peter Rosin

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