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

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Date:   Wed, 11 Apr 2018 13:01:37 +0000
From:   Jon Maloy <jon.maloy@...csson.com>
To:     Ying Xue <ying.xue@...driver.com>,
        Jia-Ju Bai <baijiaju1990@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3] net: tipc: Replace GFP_ATOMIC with GFP_KERNEL in
 tipc_mon_create



> -----Original Message-----
> From: Ying Xue [mailto:ying.xue@...driver.com]
> Sent: Wednesday, April 11, 2018 06:27
> To: Jia-Ju Bai <baijiaju1990@...il.com>; Jon Maloy
> <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>
Acked-by: Jon Maloy <jon.maloy@...csson.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);
> >