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: Thu, 30 Mar 2017 06:53:00 -0000 [thread overview]
Message-ID: <20170330065332.GA30148@gmail.com> (raw)
In-Reply-To: <20170329172510.e012406497fd38a54d5069b3@kernel.org>
* 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). There's just no way in hell we should be calling any complex
kernel function from kernel probes!
I mean, think about it, a kretprobe can be installed in a lot of places, and now
we want to call get_free_pages() from it?? This would add a massive amount of
fragility.
Instrumentation must be _simple_, every patch that adds more complexity to the
most fundamental code path of it should raise a red flag ...
So let's make this more robust, ok?
Thanks,
Ingo
next prev parent reply other threads:[~2017-03-30 6:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-29 5:21 [RFC PATCH tip/master 0/3] kprobes: tracing: kretprobe_instance dynamic allocation Masami Hiramatsu
2017-03-29 5:23 ` [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 5:24 ` [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 [this message]
2017-03-30 13:01 ` Masami Hiramatsu
2017-04-12 6:42 ` Ingo Molnar
2017-03-30 13:03 ` Alban Crequy
2017-03-29 5:25 ` [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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170330065332.GA30148@gmail.com \
--to=mingo@kernel.org \
--cc=acme@redhat.com \
--cc=alban.crequy@gmail.com \
--cc=alban@kinvolk.io \
--cc=ast@kernel.org \
--cc=corbet@lwn.net \
--cc=iago@kinvolk.io \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=lukasz.dorau@intel.com \
--cc=mhiramat@kernel.org \
--cc=michael@kinvolk.io \
--cc=mingo@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=osandov@fb.com \
--cc=rostedt@goodmis.org \
--cc=systemtap@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).