linux-kernel - Re: [PATCH 3/3] livepatch: Use static buffer for debugging messages under rq lock

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Message-ID: <alpine.LSU.2.21.1905311433230.742@pobox.suse.cz>
Date:   Fri, 31 May 2019 14:37:52 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Petr Mladek <pmladek@...e.com>
cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 3/3] livepatch: Use static buffer for debugging messages
 under rq lock

On Fri, 31 May 2019, Petr Mladek wrote:

> The err_buf array uses 128 bytes of stack space.  Move it off the stack
> by making it static.  It's safe to use a shared buffer because
> klp_try_switch_task() is called under klp_mutex.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> Acked-by: Miroslav Benes <mbenes@...e.cz>
> Reviewed-by: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.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 1bf362df76e1..5c4f0c1f826e 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -280,11 +280,11 @@ 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';
>  
> @@ -327,7 +327,6 @@ static bool klp_try_switch_task(struct task_struct *task)
>  		pr_debug("%s", err_buf);
>  
>  	return success;
> -
>  }

This could go in separately as it is not connected to the rest of the 
series.

Miroslav