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SubjectRe: [PATCH v3 13/18] of: overlay: check prevents multiple fragments touching same property
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On 10/14/18 18:06, Joe Perches wrote:
> On Sun, 2018-10-14 at 17:24 -0700, frowand.list@gmail.com wrote:
>> From: Frank Rowand <frank.rowand@sony.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

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