linux-kernel - Re: [PATCH] ia64: Pin controlling tty for unaligned fault message

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Message-ID: <544018AF.5090507@hurleysoftware.com>
Date:	Thu, 16 Oct 2014 15:12:47 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ia64: Pin controlling tty for unaligned fault message

On 10/16/2014 03:10 PM, Peter Hurley wrote:
> Prevent destruction of the controlling tty before tty_write_message()
> can determine if the tty is safe to use.

This does not make tty_write_message() bulletproof from concurrent
teardown, but that's on my todo list.


> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
> ---
>  arch/ia64/kernel/unaligned.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/ia64/kernel/unaligned.c b/arch/ia64/kernel/unaligned.c
> index 622772b..e7ae608 100644
> --- a/arch/ia64/kernel/unaligned.c
> +++ b/arch/ia64/kernel/unaligned.c
> @@ -1336,8 +1336,11 @@ ia64_handle_unaligned (unsigned long ifa, struct pt_regs *regs)
>  			 * Don't call tty_write_message() if we're in the kernel; we might
>  			 * be holding locks...
>  			 */
> -			if (user_mode(regs))
> -				tty_write_message(current->signal->tty, buf);
> +			if (user_mode(regs)) {
> +				struct tty_struct *tty = get_current_tty();
> +				tty_write_message(tty, buf);
> +				tty_kref_put(tty);
> +			}
>  			buf[len-1] = '\0';	/* drop '\r' */
>  			/* watch for command names containing %s */
>  			printk(KERN_WARNING "%s", buf);
> 

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