Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore)

[Ravi Bangoria]

On 03/15/2018 07:51 PM, Oleg Nesterov wrote:
> On 03/13, Ravi Bangoria wrote:
>> @@ -1053,6 +1056,9 @@ int uprobe_mmap(struct vm_area_struct *vma)
>>  	struct uprobe *uprobe, *u;
>>  	struct inode *inode;
>>
>> +	if (uprobe_mmap_callback)
>> +		uprobe_mmap_callback(vma);
>> +
>>  	if (no_uprobe_events() || !valid_vma(vma, true))
>>  		return 0;
> probe_event_enable() does
>
> 	uprobe_register();
> 	/* WINDOW */
> 	sdt_increment_ref_ctr();
>
> what if uprobe_mmap() is called in between? The counter(s) in this vma
> will be incremented twice, no?

I guess, it's a valid issue with PATCH 5 but should be taken care by PATCH 6.

>
>> +static struct vm_area_struct *
>> +sdt_find_vma(struct mm_struct *mm, struct trace_uprobe *tu)
>> +{
>> +	struct vm_area_struct *tmp;
>> +
>> +	for (tmp = mm->mmap; tmp != NULL; tmp = tmp->vm_next)
>> +		if (sdt_valid_vma(tu, tmp))
>> +			return tmp;
>> +
>> +	return NULL;
> I can't understand the logic... Lets ignore sdt_valid_vma() for now.
> The caller has uprobe_map_info, why it can't simply do
> vma = find_vma(uprobe_map_info->vaddr)? and then check sdt_valid_vma().

Yes. that should work. Will change it.

Thanks for the review,
Ravi