linux-kernel - RE: [PATCH] x86/resctrl: Fix return code in mkdir_rdt

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Message-ID: <TYAPR01MB63308EDD28ABD3666D6AAE168BA89@TYAPR01MB6330.jpnprd01.prod.outlook.com>
Date:   Tue, 28 Sep 2021 04:44:29 +0000
From:   "tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>
To:     'Reinette Chatre' <reinette.chatre@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] x86/resctrl: Fix return code in mkdir_rdt_prepare()

Hi Reinette,

> On 9/24/2021 1:17 AM, Shaopeng Tan wrote:
> > When kzalloc fails, we should return ENOMEM instead of ENOSPC.
> >
> > Signed-off-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> > ---
> > Hello,
> >
> > I just noticed this when I read the code.
> >
> > Thanks,
> >
> >   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > index b57b3db9a6a7..a92d047476f6 100644
> > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > @@ -2854,7 +2854,7 @@ static int mkdir_rdt_prepare(struct kernfs_node
> *parent_kn,
> >   	/* allocate the rdtgroup. */
> >   	rdtgrp = kzalloc(sizeof(*rdtgrp), GFP_KERNEL);
> >   	if (!rdtgrp) {
> > -		ret = -ENOSPC;
> > +		ret = -ENOMEM;
> >   		rdt_last_cmd_puts("Kernel out of memory\n");
> >   		goto out_unlock;
> >   	}
> >
> 
> I do not know the original motivation for using ENOSPC but from what I can tell
> this error is propagated all the way to user space. This change thus has the
> consequence that any interface built on top of resctrl could be impacted.
> 
> Is there a specific issue that you are aiming to fix here?

I didn't detect any problem on machine, I noticed it by reading at the code. 

Elsewhere in resctrl code, if kzalloc fails, it returns ENOMEM.  
For example, in the same file(rdtgroup.c), 
2107         s = kzalloc(sizeof(*s), GFP_KERNEL); 
2108         if (!s) 
2109                 return -ENOMEM; 
so, I thought it wasn't intentionally to return ENOSPC. 

As you said it maybe impact user space,  
so, please ignore this patch if you don't think it needs to be changed. 

Thanks, 
Tan Shaopeng