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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,
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        corbet@lwn.net, dan.j.williams@intel.com,
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        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>
 <20180314165943.GA5948@redhat.com>
From:   Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Date:   Thu, 15 Mar 2018 16:53:40 +0530
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On 03/14/2018 10:29 PM, Oleg Nesterov wrote:
> On 03/13, Ravi Bangoria wrote:
>> +static bool sdt_valid_vma(struct trace_uprobe *tu, struct vm_area_struct *vma)
>> +{
>> +	unsigned long vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
>> +
>> +	return tu->ref_ctr_offset &&
>> +		vma->vm_file &&
>> +		file_inode(vma->vm_file) == tu->inode &&
>> +		vma->vm_flags & VM_WRITE &&
>> +		vma->vm_start <= vaddr &&
>> +		vma->vm_end > vaddr;
>> +}
> Perhaps in this case a simple
>
> 		ref_ctr_offset < vma->vm_end - vma->vm_start
>
> check without vma_offset_to_vaddr() makes more sense, but I won't insist.
>

Hmm... I'm not quite sure. Will rethink and get back to you.

>
>> +static void sdt_increment_ref_ctr(struct trace_uprobe *tu)
>> +{
>> +	struct uprobe_map_info *info;
>> +	struct vm_area_struct *vma;
>> +	unsigned long vaddr;
>> +
>> +	uprobe_start_dup_mmap();
>> +	info = uprobe_build_map_info(tu->inode->i_mapping,
>> +				tu->ref_ctr_offset, false);
> Hmm. This doesn't look right.
>
> If you need to find all mappings (and avoid the races with fork/dup_mmap) you
> need to take this semaphore for writing, uprobe_start_dup_mmap() can't help.

Oops. Yes. Will change it.

Thanks for the review :)
Ravi