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

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Message-Id: <e802ce35-7134-ea12-774b-512546953c47@linux.vnet.ibm.com>
Date:   Thu, 15 Mar 2018 16:53:40 +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,
        naveen.n.rao@...ux.vnet.ibm.com, pc@...ibm.com,
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        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 03/14/2018 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