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

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Message-Id: <663244e6-2de0-48bb-08d1-fbc66b3c736b@linux.vnet.ibm.com>
Date:   Fri, 16 Mar 2018 17:16:49 +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,
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        gregkh@...uxfoundation.org, huawei.libin@...wei.com,
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        kirill.shutemov@...ux.intel.com, kjlx@...pleofstupid.com,
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        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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        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 03/16/2018 05:09 PM, Oleg Nesterov wrote:
> On 03/16, Ravi Bangoria wrote:
>> On 03/15/2018 08:00 PM, Oleg Nesterov wrote:
>>> 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.
> Not at all.
>
> Once build_map_info() returns any mapping can go away. Otherwise, why do
> you think the caller has to take ->mmap_sem and use find_vma()? If you
> were right, build_map_info() could just return the list of vma's instead
> of list of mm's.

Oh.. okay.. I was under wrong impression then. Will add a check there.

Thanks for the review :)
Ravi