(2013/07/03 7:23), Oleg Nesterov wrote:
> On 07/02, Oleg Nesterov wrote:
>>
>> So please ignore modules ;)
>
> Or lets discuss the change above.
No, I think this still doesn't ensure that we can remove dynamic
event safely. Since the event is related to several files under
events/ dir and buffer instances, someone can just stay open the
files while the event is removed and read/write it.
Perhaps, we need per-event_call refcounter not per-trace_array
one, and do as below.
Open file:
-> lock event_mutex
-> find event_call and event_file
-> get event_call
-> unlock event_mutex
Close:
-> lock event_mutex
-> put event_call
-> unlock event_mutex
Remove event (via kprobe_events):
-> lock event_mutex
-> find event_call
-> -EBUSY if event is enabled or refcount != 0
(here, no one accessing the event and not enabled)
-> unregister_kprobe
-> remove event
-> unlock event_mutex
The key is holding event_mutex *and* getting refcount
under any operation.
And of course, we can unregister the kprobe outside of
the event_mutex, but it still need a synchronize_sched
for safety.
-> lock event_mutex
-> wait_for_rcu (to ensure no disabled kprobe accesses the event)
-> find event_call
-> -EBUSY if event is enabled or refcount != 0
(here, no one accessing the event and not enabled)
-> remove event
-> unlock event_mutex
-> unregister_kprobe
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: [email protected]
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