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

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Message-ID: <20180315143044.GA19643@redhat.com>
Date:   Thu, 15 Mar 2018 15:30:45 +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,
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        jolsa@...hat.com, kan.liang@...el.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 03/15, Oleg Nesterov wrote:
>
> > +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().

Note to mention that sdt_find_vma() can return NULL but the callers do
vma_offset_to_vaddr(vma) without any check.

Oleg.