linux-kernel - Re: [PATCH v4 1/4] sysctl: Add register_sysctl

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Date:   Fri, 29 May 2020 11:31:24 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Xiaoming Ni <nixiaoming@...wei.com>
Cc:     keescook@...omium.org, yzaikin@...gle.com, adobriyan@...il.com,
        mingo@...nel.org, gpiccoli@...onical.com, rdna@...com,
        patrick.bellasi@....com, sfr@...b.auug.org.au,
        akpm@...ux-foundation.org, mhocko@...e.com,
        penguin-kernel@...ove.sakura.ne.jp, vbabka@...e.cz,
        tglx@...utronix.de, peterz@...radead.org,
        Jisheng.Zhang@...aptics.com, khlebnikov@...dex-team.ru,
        bigeasy@...utronix.de, pmladek@...e.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        wangle6@...wei.com, alex.huangjianhui@...wei.com
Subject: Re: [PATCH v4 1/4] sysctl: Add register_sysctl_init() interface

On Fri, May 29, 2020 at 04:33:01PM +0800, Xiaoming Ni wrote:
> On 2020/5/29 15:36, Luis Chamberlain wrote:
> > On Fri, May 29, 2020 at 03:27:22PM +0800, Xiaoming Ni wrote:
> > > On 2020/5/29 15:09, Luis Chamberlain wrote:
> > > > On Tue, May 19, 2020 at 11:31:08AM +0800, Xiaoming Ni wrote:
> > > > > --- a/kernel/sysctl.c
> > > > > +++ b/kernel/sysctl.c
> > > > > @@ -3358,6 +3358,25 @@ int __init sysctl_init(void)
> > > > >    	kmemleak_not_leak(hdr);
> > > > >    	return 0;
> > > > >    }
> > > > > +
> > > > > +/*
> > > > > + * The sysctl interface is used to modify the interface value,
> > > > > + * but the feature interface has default values. Even if register_sysctl fails,
> > > > > + * the feature body function can also run. At the same time, malloc small
> > > > > + * fragment of memory during the system initialization phase, almost does
> > > > > + * not fail. Therefore, the function return is designed as void
> > > > > + */
> > > > 
> > > > Let's use kdoc while at it. Can you convert this to proper kdoc?
> > > > 
> > > Sorry, I do n’t know the format requirements of Kdoc, can you give me some
> > > tips for writing?
> > 
> > Sure, include/net/mac80211.h is a good example.
> > 
> > > > > +void __init register_sysctl_init(const char *path, struct ctl_table *table,
> > > > > +				 const char *table_name)
> > > > > +{
> > > > > +	struct ctl_table_header *hdr = register_sysctl(path, table);
> > > > > +
> > > > > +	if (unlikely(!hdr)) {
> > > > > +		pr_err("failed when register_sysctl %s to %s\n", table_name, path);
> > > > > +		return;
> > > > 
> > > > table_name is only used for this, however we can easily just make
> > > > another _register_sysctl_init() helper first, and then use a macro
> > > > which will concatenate this to something useful if you want to print
> > > > a string. I see no point in the description for this, specially since
> > > > the way it was used was not to be descriptive, but instead just a name
> > > > followed by some underscore and something else.
> > > > 
> > > Good idea, I will fix and send the patch to you as soon as possible
> > 
> > No rush :)
> > 
> > > > > +	}
> > > > > +	kmemleak_not_leak(hdr);
> > > > 
> > > > Is it *wrong* to run kmemleak_not_leak() when hdr was not allocated?
> > > > If so, can you fix the sysctl __init call itself?
> > > I don't understand here, do you mean that register_sysctl_init () does not
> > > need to call kmemleak_not_leak (hdr), or does it mean to add check hdr
> > > before calling kmemleak_not_leak (hdr) in sysctl_init ()?
> > 
> > I'm asking that the way you are adding it, you don't run
> > kmemleak_not_leak(hdr) if the hdr allocation filed. If that is
> > right then it seems that sysctl_init() might not be doing it
> > right.
> > 
> > Can that code be shared somehow?
> > 
> >    Luis
> 
> void __ref kmemleak_not_leak(const void *ptr)
> {
> 	pr_debug("%s(0x%p)\n", __func__, ptr);
> 
> 	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
> 		make_gray_object((unsigned long)ptr);
> }
> EXPORT_SYMBOL(kmemleak_not_leak);
> 
> In the code of kmemleak_not_leak(), it is verified that the pointer is
> valid, so kmemleak_not_leak (NULL) will not be a problem.
> At the same time, there is no need to call kmemleak_not_leak() in the failed
> branch of register_sysctl_init().

Thanks for the confirmation.

   Luis