From: Ingo Molnar <mingo@kernel•org>
To: Masami Hiramatsu <mhiramat@kernel•org>
Cc: Steven Rostedt <rostedt@goodmis•org>,
Ingo Molnar <mingo@redhat•com>,
Alban Crequy <alban.crequy@gmail•com>,
Alban Crequy <alban@kinvolk•io>,
Alexei Starovoitov <ast@kernel•org>,
Jonathan Corbet <corbet@lwn•net>,
Arnaldo Carvalho de Melo <acme@redhat•com>,
Omar Sandoval <osandov@fb•com>,
linux-doc@vger•kernel.org, netdev@vger•kernel.org,
linux-kernel@vger•kernel.org, iago@kinvolk•io,
michael@kinvolk•io, Dorau Lukasz <lukasz.dorau@intel•com>,
systemtap@sourceware•org
Subject: Re: [RFC PATCH tip/master 2/3] kprobes: Allocate kretprobe instance if its free list is empty
Date: Wed, 12 Apr 2017 08:42:26 +0200 [thread overview]
Message-ID: <20170412064226.GA7737@gmail.com> (raw)
In-Reply-To: <20170330220134.448b65b9102edcf8ba1a2c81@kernel.org>
* Masami Hiramatsu <mhiramat@kernel•org> wrote:
> On Thu, 30 Mar 2017 08:53:32 +0200
> Ingo Molnar <mingo@kernel•org> wrote:
>
> >
> > * Masami Hiramatsu <mhiramat@kernel•org> wrote:
> >
> > > > So this is something I missed while the original code was merged, but the concept
> > > > looks a bit weird: why do we do any "allocation" while a handler is executing?
> > > >
> > > > That's fundamentally fragile. What's the maximum number of parallel
> > > > 'kretprobe_instance' required per kretprobe - one per CPU?
> > >
> > > It depends on the place where we put the probe. If the probed function will be
> > > blocked (yield to other tasks), then we need a same number of threads on
> > > the system which can invoke the function. So, ultimately, it is same
> > > as function_graph tracer, we need it for each thread.
> >
> > So then put it into task_struct (assuming there's no kretprobe-inside-kretprobe
> > nesting allowed).
>
> No, that is possible to put several kretprobes on same thread, e.g.
> the func1() is called from func2(), user can put kretprobes for each
> function at same time.
> So the possible solution is to allocate new return-stack for each task_struct,
> and that is what the function-graph tracer did.
>
> Anyway, I'm considering to integrate kretprobe_instance with the ret_stack.
> It will increase memory usage for kretprobes, but can provide safer way
> to allocate kretprobe_instance.
Ok, that sounds good to me.
Thanks,
Ingo
next prev parent reply other threads:[~2017-04-12 6:42 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-29 5:20 [RFC PATCH tip/master 0/3] kprobes: tracing: kretprobe_instance dynamic allocation Masami Hiramatsu
2017-03-29 5:22 ` [RFC PATCH tip/master 1/3] trace: kprobes: Show sum of probe/retprobe nmissed count Masami Hiramatsu
2017-03-31 9:45 ` Alban Crequy
2017-03-29 5:23 ` [RFC PATCH tip/master 2/3] kprobes: Allocate kretprobe instance if its free list is empty Masami Hiramatsu
2017-03-29 6:30 ` Ingo Molnar
2017-03-29 8:25 ` Masami Hiramatsu
2017-03-29 17:18 ` Josh Stone
2017-03-30 0:39 ` Masami Hiramatsu
2017-03-30 6:53 ` Ingo Molnar
2017-03-30 13:01 ` Masami Hiramatsu
2017-04-12 6:42 ` Ingo Molnar [this message]
2017-03-30 13:03 ` Alban Crequy
2017-03-29 5:24 ` [RFC PATCH tip/master 3/3] kprobes: Limit kretprobe maximum instances Masami Hiramatsu
2017-03-29 13:27 ` [RFC PATCH tip/master 0/3] kprobes: tracing: kretprobe_instance dynamic allocation Frank Ch. Eigler
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