Re: [PATCH 0/3] ftrace: handle kernel code remove

[Ingo Molnar <mingo@elte.hu>]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> The dynamic ftrace feature keeps a table of all the places that call 
> mcount to either disable them (replacing them with nops) or to enable 
> them (calling some trace function).
> 
> This table of functions is also displayed to the user interface to let 
> users enable or disable specific functions. This allows users to only 
> trace some functions within the kernel.
> 
> When a module or init sections are removed, the pointers to their 
> locations still exist in this table.  To protect against faults and 
> writing over other text, fault handling and code comparing is done. 
> When the code is update, the code being replaced is calculated and 
> compared to the actual text that is being replaced, if the code does 
> not match what is expected to be there, the change is not made.
> 
> There is a very small chance that the wrong text (or perhaps a data 
> section) could match the call to mcount and an inappropriate 
> modification could be made.
> 
> This patch series adds ftrace_release, to allow a module to remove the 
> pointers to the mcount callers in the module from this table.
> 
> Also, __init has "notrace" added to it so that text in the init 
> section are not traced. The trace currently can not be enabled until 
> after init anyway, so this should not be a problem.

applied to tip/tracing/ftrace - thanks Steve! I merged it into 
tip/master and started testing it.

	Ingo