Re: [PATCH v2] register_console: prevent adding the same console twice

["Andreas Bießmann" <andreas@biessmann.de>]

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Am 2013-03-25 09:59, schrieb Andreas Bießmann:
> This patch guards the console_drivers list to be corrupted. The
> for_each_console() macro insist on a strictly forward list ended by 
> NULL:
> 
>  con0->next->con1->next->NULL
> 
> Without this patch it may happen easily to destroy this list for 
> example by
> adding 'earlyprintk' twice, especially on embedded devices where the 
> early
> console is often a single static instance.  This will result in the 
> following
> list:
> 
>  con0->next->con0
> 
> This in turn will result in an endless loop in console_unlock() later 
> on by
> printing the first __log_buf line endlessly.
> 
> Signed-off-by: Andreas Bießmann <andreas@biessmann.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Kay Sievers <kay@vrfy.org>
> Cc: Ben Hutchings <ben@decadent.org.uk>
> Cc: stable@kernel.org
> ---
> since v1:
>  * use WARN() as Ben suggested
>  * print 'already registered' instead of 'prevent registering'
> 
>  kernel/printk.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/printk.c b/kernel/printk.c
> index abbdd9e..180ee25 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -2214,6 +2214,13 @@ void register_console(struct console *newcon)
>  	unsigned long flags;
>  	struct console *bcon = NULL;
> 
> +	if (console_drivers)
> +		for_each_console(bcon)
> +			if (WARN(bcon == newcon,
> +					"console '%s%d' already registered\n",
> +					bcon->name, bcon->index))
> +				return;
> +
>  	/*
>  	 * before we register a new CON_BOOT console, make sure we don't
>  	 * already have a valid console