netdev - Re: [PATCH v3] net: tipc: Replace GFP_ATOMIC with GFP_KERNEL in tipc_mon

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Message-ID: <7bf48d79-54fe-421a-e04c-f2d6cd2c71e2@windriver.com>
Date:   Wed, 11 Apr 2018 18:26:42 +0800
From:   Ying Xue <ying.xue@...driver.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, <jon.maloy@...csson.com>,
        <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <tipc-discussion@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] net: tipc: Replace GFP_ATOMIC with GFP_KERNEL in
 tipc_mon_create

On 04/11/2018 06:24 PM, Jia-Ju Bai wrote:
> tipc_mon_create() is never called in atomic context.
> 
> The call chain ending up at tipc_mon_create() is:
> [1] tipc_mon_create() <- tipc_enable_bearer() <- tipc_nl_bearer_enable()
> tipc_nl_bearer_enable() calls rtnl_lock(), which indicates this function
> is not called in atomic context.
> 
> Despite never getting called from atomic context,
> tipc_mon_create() calls kzalloc() with GFP_ATOMIC,
> which does not sleep for allocation.
> GFP_ATOMIC is not necessary and can be replaced with GFP_KERNEL,
> which can sleep and improve the possibility of successful allocation.
> 
> This is found by a static analysis tool named DCNS written by myself.
> And I also manually check it.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>

Acked-by: Ying Xue <ying.xue@...driver.com>

> ---
> v2:
> * Modify the description of GFP_ATOMIC in v1.
>   Thank Eric for good advice.
> v3:
> * Modify wrong text in description in v2.
>   Thank Ying for good advice.
> ---
>  net/tipc/monitor.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/net/tipc/monitor.c b/net/tipc/monitor.c
> index 9e109bb..9714d80 100644
> --- a/net/tipc/monitor.c
> +++ b/net/tipc/monitor.c
> @@ -604,9 +604,9 @@ int tipc_mon_create(struct net *net, int bearer_id)
>  	if (tn->monitors[bearer_id])
>  		return 0;
>  
> -	mon = kzalloc(sizeof(*mon), GFP_ATOMIC);
> -	self = kzalloc(sizeof(*self), GFP_ATOMIC);
> -	dom = kzalloc(sizeof(*dom), GFP_ATOMIC);
> +	mon = kzalloc(sizeof(*mon), GFP_KERNEL);
> +	self = kzalloc(sizeof(*self), GFP_KERNEL);
> +	dom = kzalloc(sizeof(*dom), GFP_KERNEL);
>  	if (!mon || !self || !dom) {
>  		kfree(mon);
>  		kfree(self);
>