linux-kernel - Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm

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Message-ID: <4DD19D10.3000201@gmail.com>
Date:	Mon, 16 May 2011 23:54:24 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	John Stultz <john.stultz@...aro.org>
CC:	LKML <linux-kernel@...r.kernel.org>, Ted Ts'o <tytso@....edu>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm

On 05/16/2011 11:19 PM, John Stultz wrote:
> Accessing task->comm requires proper locking. However in the past
> access to current->comm could be done without locking. This
> is no longer the case, so all comm access needs to be done
> while holding the comm_lock.
> 
> In my attempt to clean up unprotected comm access, I've noticed
> most comm access is done for printk output. To simplify correct
> locking in these cases, I've introduced a new %ptc format,
> which will print the corresponding task's comm.
> 
> Example use:
> printk("%ptc: unaligned epc - sending SIGBUS.\n", current);
> 
> CC: Ted Ts'o <tytso@....edu>
> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> CC: David Rientjes <rientjes@...gle.com>
> CC: Dave Hansen <dave@...ux.vnet.ibm.com>
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: linux-mm@...ck.org
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
>  lib/vsprintf.c |   24 ++++++++++++++++++++++++
>  1 files changed, 24 insertions(+), 0 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index bc0ac6b..b7a9953 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -797,6 +797,23 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
>  	return string(buf, end, uuid, spec);
>  }
>  
> +static noinline_for_stack

Actually, why noinline? Did your previous version have there some
TASK_COMM_LEN buffer or anything on stack which is not there anymore?

> +char *task_comm_string(char *buf, char *end, void *addr,
> +			 struct printf_spec spec, const char *fmt)
> +{
> +	struct task_struct *tsk = addr;
> +	char *ret;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&tsk->comm_lock, flags);
> +	ret = string(buf, end, tsk->comm, spec);
> +	spin_unlock_irqrestore(&tsk->comm_lock, flags);
> +
> +	return ret;
> +}
> +
> +
> +
>  int kptr_restrict = 1;
>  
>  /*

thanks,
-- 
js
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