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Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     mhiramat@kernel.org, peterz@infradead.org,
        srikar@linux.vnet.ibm.com, acme@kernel.org,
        ananth@linux.vnet.ibm.com, akpm@linux-foundation.org,
        alexander.shishkin@linux.intel.com, alexis.berlemont@gmail.com,
        corbet@lwn.net, dan.j.williams@intel.com,
        gregkh@linuxfoundation.org, huawei.libin@huawei.com,
        hughd@google.com, jack@suse.cz, jglisse@redhat.com,
        jolsa@redhat.com, kan.liang@intel.com,
        kirill.shutemov@linux.intel.com, kjlx@templeofstupid.com,
        kstewart@linuxfoundation.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com,
        milian.wolff@kdab.com, mingo@redhat.com, namhyung@kernel.org,
        naveen.n.rao@linux.vnet.ibm.com, pc@us.ibm.com,
        pombredanne@nexb.com, rostedt@goodmis.org, tglx@linutronix.de,
        tmricht@linux.vnet.ibm.com, willy@infradead.org,
        yao.jin@linux.intel.com, fengguang.wu@intel.com,
        Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
References: <20180313125603.19819-1-ravi.bangoria@linux.vnet.ibm.com>
 <20180313125603.19819-6-ravi.bangoria@linux.vnet.ibm.com>
 <20180315142120.GA19218@redhat.com>
From:   Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Date:   Fri, 16 Mar 2018 14:51:52 +0530
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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