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

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Message-Id: <3b303a2d-35dd-9178-fc03-de9f2d588797@linux.vnet.ibm.com>
Date:   Fri, 16 Mar 2018 14:58:55 +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 03/15/2018 08:00 PM, Oleg Nesterov wrote:
> On 03/15, Oleg Nesterov wrote:
>>> +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().
> Note to mention that sdt_find_vma() can return NULL but the callers do
> vma_offset_to_vaddr(vma) without any check.

If the "mm" we are passing to sdt_find_vma() is returned by
uprobe_build_map_info(ref_ctr_offset), sdt_find_vma() must
_not_ return NULL.

Thanks for the review,
Ravi