linux-kernel - Re: [RFC PATCH v2 for 4.15 08/14] Provide cpu

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Message-ID: <444885121.6172.1510022437259.JavaMail.zimbra@efficios.com>
Date:   Tue, 7 Nov 2017 02:40:37 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [RFC PATCH v2 for 4.15 08/14] Provide cpu_opv system call

----- On Nov 6, 2017, at 9:07 PM, Boqun Feng boqun.feng@...il.com wrote:

> On Mon, Nov 06, 2017 at 03:56:38PM -0500, Mathieu Desnoyers wrote:
> [...]
>> +static int cpu_op_pin_pages(unsigned long addr, unsigned long len,
>> +		struct page ***pinned_pages_ptr, size_t *nr_pinned,
>> +		int write)
>> +{
>> +	struct page *pages[2];
>> +	int ret, nr_pages;
>> +
>> +	if (!len)
>> +		return 0;
>> +	nr_pages = cpu_op_range_nr_pages(addr, len);
>> +	BUG_ON(nr_pages > 2);
>> +	if (*nr_pinned + nr_pages > NR_PINNED_PAGES_ON_STACK) {
> 
> Is this a bug? Seems you will kzalloc() every time if *nr_pinned is
> bigger than NR_PINNED_PAGES_ON_STACK, which will result in memory
> leaking.
> 
> I think the logic here is complex enough for us to introduce a
> structure, like:
> 
>	struct cpu_opv_page_pinner {
>		int nr_pinned;
>		bool is_kmalloc;
>		struct page **pinned_pages;
>	};
> 
> Thoughts?

Good catch !

How about the attached diff ? I'll fold it into the rseq/dev tree.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

View attachment "fix-cpu-opv-leak.patch" of type "text/x-patch" (5793 bytes)