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

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Date:   Thu, 15 Mar 2018 15:21:20 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.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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        kstewart@...uxfoundation.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
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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 03/13, Ravi Bangoria wrote:
>
> @@ -1053,6 +1056,9 @@ int uprobe_mmap(struct vm_area_struct *vma)
>  	struct uprobe *uprobe, *u;
>  	struct inode *inode;
>
> +	if (uprobe_mmap_callback)
> +		uprobe_mmap_callback(vma);
> +
>  	if (no_uprobe_events() || !valid_vma(vma, true))
>  		return 0;

probe_event_enable() does

	uprobe_register();
	/* WINDOW */
	sdt_increment_ref_ctr();

what if uprobe_mmap() is called in between? The counter(s) in this vma
will be incremented twice, no?

> +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().

Oleg.