linux-kernel - Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore)

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Date:   Mon, 13 Aug 2018 10:12:14 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>, mhiramat@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org,
        open list <linux-kernel@...r.kernel.org>,
        ananth@...ux.vnet.ibm.com,
        Alexis Berlemont <alexis.berlemont@...il.com>,
        naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com
Subject: Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference
 count (semaphore)

On Mon, Aug 13, 2018 at 6:17 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 08/13, Ravi Bangoria wrote:
>>
>> > But damn, process creation (exec) is trivial. We could add a new uprobe_exec()
>> > hook and avoid delayed_uprobe_install() in uprobe_mmap().
>>
>> I'm sorry. I didn't get this.
>
> Sorry for confusion...
>
> I meant, if only exec*( could race with _register(), we could add another uprobe
> hook which updates all (delayed) counters before return to user-mode.
>
>> > Afaics, the really problematic case is dlopen() which can race with _register()
>> > too, right?
>>
>> dlopen() should internally use mmap() right? So what is the problem here? Can
>> you please elaborate.
>
> What I tried to say is that we can't avoid uprobe_mmap()->delayed_uprobe_install()
> because dlopen() can race with _register() too, just like exec.
>
> Oleg.
>

How about we do delayed_uprobe_install() per file? Say we keep a list
of delayed_uprobe
in load_elf_binary(). Then we can install delayed_uprobe after loading
all sections of the
file.

Song