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

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Message-Id: <56ae982d-2fbf-09c4-989b-57bce5a1cb04@linux.vnet.ibm.com>
Date:   Fri, 16 Mar 2018 14:51:52 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     mhiramat@...nel.org, peterz@...radead.org,
        srikar@...ux.vnet.ibm.com, acme@...nel.org,
        ananth@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        alexander.shishkin@...ux.intel.com, alexis.berlemont@...il.com,
        corbet@....net, dan.j.williams@...el.com,
        gregkh@...uxfoundation.org, huawei.libin@...wei.com,
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        jolsa@...hat.com, kan.liang@...el.com,
        kirill.shutemov@...ux.intel.com, kjlx@...pleofstupid.com,
        kstewart@...uxfoundation.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        milian.wolff@...b.com, mingo@...hat.com, namhyung@...nel.org,
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        pombredanne@...b.com, rostedt@...dmis.org, tglx@...utronix.de,
        tmricht@...ux.vnet.ibm.com, willy@...radead.org,
        yao.jin@...ux.intel.com, fengguang.wu@...el.com,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)



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