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Date: Thu, 15 Mar 2018 15:21:20 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Cc: mhiramat@kernel.org, peterz@infradead.org, srikar@linux.vnet.ibm.com,
	acme@kernel.org, ananth@linux.vnet.ibm.com,
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Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)
Message-ID: <20180315142120.GA19218@redhat.com>
References: <20180313125603.19819-1-ravi.bangoria@linux.vnet.ibm.com>
 <20180313125603.19819-6-ravi.bangoria@linux.vnet.ibm.com>
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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.