(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: [email protected]
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