linux-kernel - Re: [PATCH v18 49/80] c/r: support for UTS namespace

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Message-ID: <20090929185126.GB13297@us.ibm.com>
Date:	Tue, 29 Sep 2009 13:51:26 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	"Nikita V. Youshchenko" <yoush@...msu.su>
Cc:	Oren Laadan <orenl@...rato.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Dan Smith <danms@...ibm.com>,
	Oren Laadan <orenl@...columbia.edu>
Subject: Re: [PATCH v18 49/80] c/r: support for UTS namespace

Quoting Nikita V. Youshchenko (yoush@...msu.su):
> > +static struct uts_namespace *do_restore_uts_ns(struct ckpt_ctx *ctx)
> > ...
> > +#ifdef CONFIG_UTS_NS
> > +	uts_ns = create_uts_ns();
> > +	if (!uts_ns) {
> > +		uts_ns = ERR_PTR(-ENOMEM);
> > +		goto out;
> > +	}
> > +	down_read(&uts_sem);
> > +	name = &uts_ns->name;
> > +	memcpy(name->sysname, h->sysname, sizeof(name->sysname));
> > +	memcpy(name->nodename, h->nodename, sizeof(name->nodename));
> > +	memcpy(name->release, h->release, sizeof(name->release));
> > +	memcpy(name->version, h->version, sizeof(name->version));
> > +	memcpy(name->machine, h->machine, sizeof(name->machine));
> > +	memcpy(name->domainname, h->domainname, sizeof(name->domainname));
> > +	up_read(&uts_sem);
> 
> Could you please explain what for is this down_read() / up_read() ?
> You operate only on local objects: 'name' points to just-created 
> uts_ns, 'h' is also local data.

Yup, good point, that looks unnecessary.

thanks,
-serge
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