linux-kernel - Re: [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening probe event files and deleting probe

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Date:	Fri, 12 Jul 2013 22:09:50 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening
 probe event files and deleting probe

(2013/07/04 12:33), Steven Rostedt wrote:
> Currently there exists a race with deleting a kprobe or uprobe and
> a user opening the probe event file or using perf events.
> 
> The problem stems from not being able to take the probe_lock from the
> unregister code because we may have the event_mutex at the time, and
> the event mutex may be taken with the probe_lock held.
> 
> To solve this, the events get a ref count (using the flags field), where
> when an event file is opened, the ftrace_event_call ref count increments.
> Then this is checked under event_mutex and if set, the unregistering
> of the probe will fail.
> 
> Here's a test that shows how things break:
> 
>      # cd /sys/kernel/debug/tracing
>      # echo 'p:sigprocmask sigprocmask' > kprobe_events || exit -1
>      # enable_probe() {
>         sleep 10
>         echo 1
>      }
>      # file=events/kprobes/sigprocmask/enable
>      # enable_probe > $file &
>      > kprobe_events
>     
>     The above will corrupt the kprobe system, as the write to the enable
>     file will happen after the kprobe was deleted.
>     
>     Trying to create the probe again fails:
>     
>      # echo 'p:sigprocmask sigprocmask' > kprobe_events
>      # cat kprobe_events
>     p:kprobes/sigprocmask sigprocmask
>      # ls events/kprobes/
>     enable  filter
> 
> After applying these patches, the "> kprobe_events" fails due to the
> event being busy.
> 
> Masami, please review these patches and give your ack.

Steve, Oleg, could you also take a look on my additional 2 patches too?

I think both this series and my patches are required for
fixing most of the problem. (what we need is a patch to ensure
finishing all running uprobe handlers at disabling it *if needed*)

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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