linux-kernel - Re: [PATCH] x86/mm/pat: Do a small optimization in reserve

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Message-ID: <20150721153107.GD7434@nazgul.tnic>
Date:	Tue, 21 Jul 2015 17:31:07 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Pan Xinhui <xinhuix.pan@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, toshi.kani@...com, jgross@...e.com,
	mcgrof@...e.com, "mnipxh@....com" <mnipxh@....com>
Subject: Re: [PATCH] x86/mm/pat: Do a small optimization in reserve_memtype

On Tue, Jul 21, 2015 at 03:32:50PM +0800, Pan Xinhui wrote:
> yes, we may access an freed memory at that time. Because entry is
> stored in rb-tree. Need lock when we access it.

Ah, we touch entry, right.

> > improve the comments over memtype_lock to explain what exactly it protects.
> > 
> lock is needed when we access the data stored in rb-tree. :)

I didn't ask you what it protects - I can do my own grepping and read
pat_rbtree.c just fine - I asked you to update the comment.

> I find another bug, although it's very hard to hit.
> just in reserve_memtype()
> ----------------------------------
>         err = rbt_memtype_check_insert(new, new_type);
>         if (err) {
>                 printk(KERN_INFO "reserve_memtype failed [mem %#010Lx-%#010Lx], track %s, req %s\n",
>                        start, end - 1,
>                        cattr_name(new->type), cattr_name(req_type));
>                 kfree(new);
>                 spin_unlock(&memtype_lock);
> 
>                 return err;
>         }
> 
>         spin_unlock(&memtype_lock); //this unlock may cause problems because the next dprintk access *new*

Yes.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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