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

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Date:   Mon, 13 Aug 2018 15:17:24 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     Song Liu <liu.song.a23@...il.com>, 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 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.