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

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Message-ID: <20180314165943.GA5948@redhat.com>
Date:   Wed, 14 Mar 2018 17:59:44 +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,
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Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)

On 03/13, Ravi Bangoria wrote:
>
> +static bool sdt_valid_vma(struct trace_uprobe *tu, struct vm_area_struct *vma)
> +{
> +	unsigned long vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
> +
> +	return tu->ref_ctr_offset &&
> +		vma->vm_file &&
> +		file_inode(vma->vm_file) == tu->inode &&
> +		vma->vm_flags & VM_WRITE &&
> +		vma->vm_start <= vaddr &&
> +		vma->vm_end > vaddr;
> +}

Perhaps in this case a simple

		ref_ctr_offset < vma->vm_end - vma->vm_start

check without vma_offset_to_vaddr() makes more sense, but I won't insist.



> +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();
> +	info = uprobe_build_map_info(tu->inode->i_mapping,
> +				tu->ref_ctr_offset, false);

Hmm. This doesn't look right.

If you need to find all mappings (and avoid the races with fork/dup_mmap) you
need to take this semaphore for writing, uprobe_start_dup_mmap() can't help.

Oleg.