linux-kernel - Re: [PATCH v3 06/12] ppc64/kexec_file: restrict memory usage of kdump kernel

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Date:   Thu, 16 Jul 2020 19:03:08 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Hari Bathini <hbathini@...ux.ibm.com>
Cc:     Pingfan Liu <piliu@...hat.com>, Nayna Jain <nayna@...ux.ibm.com>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 06/12] ppc64/kexec_file: restrict memory usage of kdump kernel


Hari Bathini <hbathini@...ux.ibm.com> writes:

> On 16/07/20 4:22 am, Thiago Jung Bauermann wrote:
>> 
>> Hari Bathini <hbathini@...ux.ibm.com> writes:
>> 
>
> <snip>
>
>>> +/**
>>> + * get_node_path - Get the full path of the given node.
>>> + * @dn:            Node.
>>> + * @path:          Updated with the full path of the node.
>>> + *
>>> + * Returns nothing.
>>> + */
>>> +static void get_node_path(struct device_node *dn, char *path)
>>> +{
>>> +	if (!dn)
>>> +		return;
>>> +
>>> +	get_node_path(dn->parent, path);
>> 
>> Is it ok to do recursion in the kernel? In this case I believe it's not
>> problematic since the maximum call depth will be the maximum depth of a
>> device tree node which shouldn't be too much. Also, there are no local
>> variables in this function. But I thought it was worth mentioning.
>
> You are right. We are better off avoiding the recursion here. Will
> change it to an iterative version instead.

Ok.

>>> +	 * each representing a memory range.
>>> +	 */
>>> +	ranges = (len >> 2) / (n_mem_addr_cells + n_mem_size_cells);
>>> +
>>> +	for (i = 0; i < ranges; i++) {
>>> +		base = of_read_number(prop, n_mem_addr_cells);
>>> +		prop += n_mem_addr_cells;
>>> +		end = base + of_read_number(prop, n_mem_size_cells) - 1;
>
> prop is not used after the above.
>
>> You need to `prop += n_mem_size_cells` here.
>
> But yeah, adding it would make it look complete in some sense..

Isn't it used in the next iteration of the loop?

-- 
Thiago Jung Bauermann
IBM Linux Technology Center