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Date: Wed, 14 Mar 2018 17:59:44 +0100
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)
Message-ID: <20180314165943.GA5948@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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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, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, alexis.berlemont@gmail.com, corbet@lwn.net, dan.j.williams@intel.com, gregkh@linuxfoundation.org, huawei.libin@huawei.com, hughd@google.com, jack@suse.cz, jglisse@redhat.com, jolsa@redhat.com, kan.liang@intel.com, kirill.shutemov@linux.intel.com, kjlx@templeofstupid.com, kstewart@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, milian.wolff@kdab.com, mingo@redhat.com, namhyung@kernel.org, naveen.n.rao@linux.vnet.ibm.com, pc@us.ibm.com, pombredanne@nexb.com, rostedt@goodmis.org, tglx@linutronix.de, tmricht@linux.vnet.ibm.com, willy@infradead.org, yao.jin@linux.intel.com, fengguang.wu@intel.com

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.