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

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Message-ID: <20080815092844.GD22209@elte.hu>
Date:	Fri, 15 Aug 2008 11:28:44 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>, srostedt@...hat.com
Subject: Re: [PATCH 0/3] ftrace: handle kernel code remove


* Steven Rostedt <rostedt@...dmis.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
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