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

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Date:   Thu, 15 Mar 2018 12:48:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc:     mhiramat@...nel.org, oleg@...hat.com, 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,
        hughd@...gle.com, jack@...e.cz, jglisse@...hat.com,
        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,
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        yao.jin@...ux.intel.com, fengguang.wu@...el.com
Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)

On Tue, 13 Mar 2018 18:26:00 +0530
Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> wrote:

> +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();

Please add a comment here that this function ups the mm ref count for
each info returned. Otherwise it's hard to know what that mmput() below
matches.

-- Steve

> +	info = uprobe_build_map_info(tu->inode->i_mapping,
> +				tu->ref_ctr_offset, false);
> +	if (IS_ERR(info))
> +		goto out;
> +
> +	while (info) {
> +		down_write(&info->mm->mmap_sem);
> +
> +		vma = sdt_find_vma(info->mm, tu);
> +		vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
> +		sdt_update_ref_ctr(info->mm, vaddr, 1);
> +
> +		up_write(&info->mm->mmap_sem);
> +		mmput(info->mm);
> +		info = uprobe_free_map_info(info);
> +	}
> +
> +out:
> +	uprobe_end_dup_mmap();
> +}
> +