linux-kernel - Re: [PATCH v3 13/18] of: overlay: check prevents multiple fragments touching same property

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Date:   Sun, 14 Oct 2018 18:52:21 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Joe Perches <joe@...ches.com>, Rob Herring <robh+dt@...nel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alan Tull <atull@...nel.org>, Moritz Fischer <mdf@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        devicetree@...r.kernel.org, linux-fpga@...r.kernel.org
Subject: Re: [PATCH v3 13/18] of: overlay: check prevents multiple fragments
 touching same property

On 10/14/18 18:06, Joe Perches wrote:
> On Sun, 2018-10-14 at 17:24 -0700, frowand.list@...il.com wrote:
>> From: Frank Rowand <frank.rowand@...y.com>
>>
>> Add test case of two fragments updating the same property.  After
>> adding the test case, the system hangs at end of boot, after
>> after slub stack dumps from kfree() in crypto modprobe code.
> []
>> -static int check_changeset_dup_add_node(struct overlay_changeset *ovcs)
>> +static int changeset_dup_entry_check(struct overlay_changeset *ovcs)
>>  {
>> -	struct of_changeset_entry *ce_1, *ce_2;
>> -	char *fn_1, *fn_2;
>> -	int name_match;
>> +	struct of_changeset_entry *ce_1;
>> +	int dup_entry = 0;
>>  
>>  	list_for_each_entry(ce_1, &ovcs->cset.entries, node) {
>> -
>> -		if (ce_1->action == OF_RECONFIG_ATTACH_NODE ||
>> -		    ce_1->action == OF_RECONFIG_DETACH_NODE) {
>> -
>> -			ce_2 = ce_1;
>> -			list_for_each_entry_continue(ce_2, &ovcs->cset.entries, node) {
>> -				if (ce_2->action == OF_RECONFIG_ATTACH_NODE ||
>> -				    ce_2->action == OF_RECONFIG_DETACH_NODE) {
>> -					/* inexpensive name compare */
>> -					if (!of_node_cmp(ce_1->np->full_name,
>> -					    ce_2->np->full_name)) {
>> -						/* expensive full path name compare */
>> -						fn_1 = kasprintf(GFP_KERNEL, "%pOF", ce_1->np);
>> -						fn_2 = kasprintf(GFP_KERNEL, "%pOF", ce_2->np);
>> -						name_match = !strcmp(fn_1, fn_2);
>> -						kfree(fn_1);
>> -						kfree(fn_2);
>> -						if (name_match) {
>> -							pr_err("ERROR: multiple overlay fragments add and/or delete node %pOF\n",
>> -							       ce_1->np);
>> -							return -EINVAL;
>> -						}
>> -					}
>> -				}
>> -			}
>> -		}
>> +		dup_entry |= find_dup_cset_node_entry(ovcs, ce_1);
>> +		dup_entry |= find_dup_cset_prop(ovcs, ce_1);
> 
> I think this is worse performance than before.
> 
> This now walks all entries when before it would
> return -EINVAL directly when it found a match.

Yes, it is worse performance, but that is OK.

This is a check that is done when a devicetree overlay is applied.
If an error occurs then that means that the overlay was incorrectly
specified.  The file drivers/of/unittest-data/overlay_bad_add_dup_prop.dts
in this patch provides an example of how a bad overlay can be created.

Once an error was detected, the check could return immediately, or it
could continue to give a complete list of detected errors.  I chose to
give the complete list of detected errors.

-Frank