Messages in this thread | | | Subject | Re: [PATCHv2 02/10] ftrace: Change mcount call replacement logic | From | Steven Rostedt <> | Date | Tue, 20 Dec 2011 11:33:19 -0500 |
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On Tue, 2011-12-20 at 14:10 +0100, Jiri Olsa wrote:
> let me try with an example.. > > say we have only 2 traceable functions - A and B ;) > > 1) set global filter for function A with 'echo A > ./set_ftrace_filter' > a - A is put to the global_ops filter > > 2) enable function trace with 'echo function > current_tracer' > a - register_ftrace_function is called with function trace ftrace_ops (GLOBAL flag) > b - update_ftrace_function is called, setting ftrace_ops callback function > to be called directly from the assembly entry_* code > c - ftrace_hash_rec_enable is called, and dyn_ftrace record > for function A is updated: > A::flags|FL_MASK = 1 > d - ftrace_replace_code(1) is called, and function A is > brought in to life > > 3) enable function trace via perf ftrace_ops > a - register_ftrace_function is called with perf event ftrace_ops (!GLOBAL flag) > b - update_ftrace_function is called, setting ftrace_ops_list_func > function to be called from the assembly entry_* code and > handle the ftrace_ops' dispatch > c - ftrace_hash_rec_enable is called, and A and B dyn_ftrace records > are updated: > A::flags|FL_MASK = 2 > B::flags|FL_MASK = 1 > d - ftrace_replace_code(1) is called, and function B is > brought in to life > > 4) disable function trace via perf ftrace_ops > a - unregister_ftrace_function is called with perf event ftrace_ops (same as in step 3) > b - update_ftrace_function is called, setting global ftrace_ops (from step 2) > callback function to be called directly from the assembly entry_* code > c - ftrace_hash_rec_disable is called, and A and B dyn_ftrace > records are updated: > A::flags|FL_MASK = 1 > B::flags|FL_MASK = 0 > d - ??? see below.. > > Now, only the global function trace ftrace_ops is enabled (from step 2), > but both A and B are alive and feeding the tracer despite its filter (function A), > because its ftrace_ops is directly linked to the assembly entry_* code (step 4b). > > The reason is that even though we updated the B's dyn_ftrace record (step 4c) > to be 'B::flags|FL_MASK == 0', we did not update the B call itself and disable it. > > If we'd call ftrace_replace_code(1) at 4d), the B function would be > disabled, and we would get expected behaviour. > > So thats the reason I think we should update the calls (mcount call code) > each time we unregister the ftrace_ops, because some records could be > enabled only for the specific ftrace_ops and we need to put them down > when we disable this ftrace_ops. > > > hopefully it make any sense.. :)
Ah, OK, I am able to trigger this. I see what you mean. Yeah, now that we have a counter, it should enable/disable based on the counter. And the DISABLE is still needed for just the "disable regardless" (/proc/sys/kernel/ftrace_enabled = 0).
I'll apply your patch and see how it works. Thanks!
-- Steve
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