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Date:   Fri, 16 Mar 2018 12:39:18 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Cc:     mhiramat@kernel.org, peterz@infradead.org,
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Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)
Message-ID: <20180316113917.GA21303@redhat.com>
References: <20180313125603.19819-1-ravi.bangoria@linux.vnet.ibm.com>
 <20180313125603.19819-6-ravi.bangoria@linux.vnet.ibm.com>
 <20180315142120.GA19218@redhat.com>
 <20180315143044.GA19643@redhat.com>
 <3b303a2d-35dd-9178-fc03-de9f2d588797@linux.vnet.ibm.com>
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On 03/16, Ravi Bangoria wrote:
>
> On 03/15/2018 08:00 PM, Oleg Nesterov wrote:
> > Note to mention that sdt_find_vma() can return NULL but the callers do
> > vma_offset_to_vaddr(vma) without any check.
>
> If the "mm" we are passing to sdt_find_vma() is returned by
> uprobe_build_map_info(ref_ctr_offset), sdt_find_vma() must
> _not_ return NULL.

Not at all.

Once build_map_info() returns any mapping can go away. Otherwise, why do
you think the caller has to take ->mmap_sem and use find_vma()? If you
were right, build_map_info() could just return the list of vma's instead
of list of mm's.

Oleg.