Messages in this thread |  | | Date | Wed, 03 Jul 2013 23:33:47 -0400 | From | Steven Rostedt <> | Subject | [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening probe event files and deleting probe |
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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.
Srikar, can you please review the last patch. I didn't test uprobes with this. I'll do that after the 4th.
Thanks,
-- Steve
Oleg Nesterov (1): tracing: trace_remove_event_call() should fail if call/file is in use
Steven Rostedt (Red Hat) (3): tracing: Add ref count to ftrace_event_call tracing/kprobes: Fail to unregister if probe event files are open tracing/uprobes: Fail to unregister if probe event files are open
---- include/linux/ftrace_event.h | 8 +++- kernel/trace/trace_events.c | 109 +++++++++++++++++++++++++++++++++++++++--- kernel/trace/trace_kprobe.c | 21 +++++--- kernel/trace/trace_uprobe.c | 48 ++++++++++++++----- 4 files changed, 160 insertions(+), 26 deletions(-)
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