linux-kernel - Re: [PATCH] staging: most: video: fix registration of an empty comp core

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Date:   Wed, 05 Sep 2018 12:06:55 +0200
From:   Alexander Stein <alexander.stein@...tec-electronic.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christian Gromm <christian.gromm@...rochip.com>,
        Abdun Nihaal <abdun.nihaal@...il.com>,
        devel@...verdev.osuosl.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: most: video: fix registration of an empty comp core_component

On Wednesday, September 5, 2018, 11:46:05 AM CEST Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently we have structrues comp (which is empty) and comp_info being
> used to register and deregister the component.  This mismatch in naming
> occurred from a previous commit that renamed aim_info to comp. Fix this
> to use consistent component naming in line with most/net, most/sound etc.
> 
> This fixes the message two issues, one with a null empty name when
> loading the module:
> 
> [ 1485.269515] most_core: registered new core component (null)
> 
> and an Oops when removing the module:
> 
> [ 1485.277971] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> [ 1485.278648] PGD 0 P4D 0
> [ 1485.279253] Oops: 0002 [#2] SMP PTI
> [ 1485.279847] CPU: 1 PID: 32629 Comm: modprobe Tainted: P      D WC OE     4.18.0-8-generic #9
> [ 1485.280442] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
> [ 1485.281040] RIP: 0010:most_deregister_component+0x3c/0x70 [most_core]
> .. etc
> 
> Fixes: 1b10a0316e2d ("staging: most: video: remove aim designators")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/staging/most/video/video.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
> index cf342eb58e10..ad7e28ab9a4f 100644
> --- a/drivers/staging/most/video/video.c
> +++ b/drivers/staging/most/video/video.c
> @@ -530,7 +530,7 @@ static int comp_disconnect_channel(struct most_interface *iface,
>  	return 0;
>  }
>  
> -static struct core_component comp_info = {
> +static struct core_component comp = {
>  	.name = "video",
>  	.probe_channel = comp_probe_channel,
>  	.disconnect_channel = comp_disconnect_channel,

Doesn't it make more sense to move that variable defintion where currently the forward declaration is?
This way you can't have 2 variables accidentally. You will need forward declarations for those two functions, but a mismatch here results in a linker error rather than a runtime NULL pointer access

Best regards,
Alexander