Messages in this thread | | | Date | Tue, 3 Jun 2008 09:00:26 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 0/3][RFC] ftrace: track dynamic ftrace update failures |
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On Tue, 3 Jun 2008, Abhishek Sagar wrote: > > > Have you also taken into account adding and removing of modules? This can > > cause some funny behaviours with ftrace that can be rather dangerous. > > I've tried to accommodate them (fixed the wrong use of > kernel_text_address). This makes > init and module function records eligible to be freed. Only core > kernel function update failures now get tracked/remembered. > > There might still be a need to find a way to track external modifiers > of mcount call-sites such as (but not limited to) kprobes. Consider > this (rather long) contrived scenario: > > 1. Function foo gets recorded by ftrace. > 2. Mcount call site of foo is patched with a NOP by ftraced. > 3. foo gets 'enabled' by some ftrace filter rule. NOP changes to a > call to the function tracer. > 4. A kprobe is registered on the mcount call-site. It places a trap > generating instruction at the > mcount call site and stores the call-to-function-tracer instruction > elsewhere internally. > 5. Tracing is disabled by end user. > 6. Disabling of foo fails because Kprobe had placed a trap at the > mcount call site. > 7. foo still keeps getting traced because Kprobes will keep > single-stepping the call-to-function-tracer instruction each time the > mcount call site is executed. > > Not sure what to do with such cases...
Can we add an API to kprobes or perhaps a way to register code modification in ftrace, that ftrace can ignore? Let the two know about each other, but in a way that they dont need to know the internals of one another.
-- Steve
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