linux-kernel - Re: [PATCH v2 2/2] livepatch: Use static buffer for debugging messages under rq lock

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Message-ID: <20190507004319.oxxncicid6pxg352@treble>
Date:   Mon, 6 May 2019 19:43:19 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] livepatch: Use static buffer for debugging
 messages under rq lock

On Tue, Apr 30, 2019 at 11:10:49AM +0200, Petr Mladek wrote:
> klp_try_switch_task() is called under klp_mutex. The buffer for
> debugging messages might be static.

The patch description is missing a "why" (presumably to reduce stack
usage).

> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> ---
>  kernel/livepatch/transition.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index 8e0274075e75..d66086fd6d75 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -304,11 +304,11 @@ static int klp_check_stack(struct task_struct *task, char *err_buf)
>   */
>  static bool klp_try_switch_task(struct task_struct *task)
>  {
> +	static char err_buf[STACK_ERR_BUF_SIZE];
>  	struct rq *rq;
>  	struct rq_flags flags;
>  	int ret;
>  	bool success = false;
> -	char err_buf[STACK_ERR_BUF_SIZE];
>  
>  	err_buf[0] = '\0';
>  
> @@ -351,7 +351,6 @@ static bool klp_try_switch_task(struct task_struct *task)
>  		pr_debug("%s", err_buf);
>  
>  	return success;
> -
>  }
>  
>  /*
> -- 
> 2.16.4
> 

-- 
Josh