linux-kernel - [RFC patch 00/21] TIF_KERNEL

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Date:	Sun, 15 Mar 2009 15:03:40 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [RFC patch 00/21] TIF_KERNEL_TRACE thread flags

Hello,

This is the implementatino of TIF_KERNEL_TRACE thread flags I did in the LTTng
tree. Basically, it offers :

- Setting a per-thread flag for _all_ threads to enable system-wide syscall
  tracing.
- No performance impact when disabled, no need to stop threads upon
  activation/deactivation (does not add latency to userspace threads upon
  activation).

The most tricky bits are in the x86_64 architecture, because its entry_64.S
code does not expect the thread flags to be changed concurrently while the
thread is running. I modified entry_64.S so that the architecture does not
suffer of any performance impact when syscall audit or secure computing is
enabled, but tests for the TIF_KERNEL_TRACE flag upon return to userspace too.

Given this looks very much like what Frederic is currently doing, I think it's
good to post it for comments.

utrace tracehooks could potentially make this patchset obsolete, but I an not
yet convinced that utrace offers the same low-latency guarantees as this code.

It applies on top of kernel 2.6.29-rc7.

Mathieu

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Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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