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Re: [PATCH] Linux Kernel Markers 0.13 for 2.6.17
- From: fche at redhat dot com (Frank Ch. Eigler)
- To: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- Cc: Jeremy Fitzhardinge <jeremy at goop dot org>, Martin Bligh <mbligh at google dot com>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, prasanna at in dot ibm dot com, Andrew Morton <akpm at osdl dot org>, Ingo Molnar <mingo at elte dot hu>, Paul Mundt <lethal at linux-sh dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, Jes Sorensen <jes at sgi dot com>, Tom Zanussi <zanussi at us dot ibm dot com>, Richard J Moore <richardj_moore at uk dot ibm dot com>, Michel Dagenais <michel dot dagenais at polymtl dot ca>, Christoph Hellwig <hch at infradead dot org>, Greg Kroah-Hartman <gregkh at suse dot de>, Thomas Gleixner <tglx at linutronix dot de>, William Cohen <wcohen at redhat dot com>, ltt-dev at shafik dot org, systemtap at sources dot redhat dot com, Alan Cox <alan at lxorguk dot ukuu dot org dot uk>, Karim Yaghmour <karim at opersys dot com>, Pavel Machek <pavel at suse dot cz>, Joe Perches <joe at perches dot com>, "Randy.Dunlap" <rdunlap at xenotime dot net>, "Jose R. Santos" <jrs at us dot ibm dot com>
- Date: 26 Sep 2006 15:49:34 -0400
- Subject: Re: [PATCH] Linux Kernel Markers 0.13 for 2.6.17
- References: <20060925233349.GA2352@Krystal> <20060925235617.GA3147@Krystal> <45187146.8040302@goop.org> <20060926002551.GA18276@Krystal> <20060926004535.GA2978@Krystal> <45187C0E.1080601@goop.org> <20060926025924.GA27366@Krystal> <4518B4A0.6070509@goop.org> <20060926180414.GA10497@Krystal> <4519781D.9040503@goop.org> <20060926190849.GA2280@Krystal>
Mathieu Desnoyers <compudj@krystal.dyndns.org> writes:
> [...]
> > Yep, that looks reasonable. Though you could just directly test a
> > per-marker enable flag, rather than using "condition"...
> [...]
> I am not sure I understand your suggestion correctly.. do you mean having
> a per-marker flag that would be loaded and tested at every marker site ?
I gather that one reason for working so hard with the inline assembly
is a race condition problem with the plain STAP_MARK style of marker
disconnection:
if (pointer) (*pointer)(args ...);
Granted, but this problem could almost certainly be dealt with simpler
than that. How about a compxchg or other atomic-fetch of the static
pointer with a local variable? That should solve the worry of an
(*NULL) call.
If we then become concerned with a valid pointer become obsolete (the
probe handler function wanting to unload), we might be able to use
some RCU-type deferral mechanism and/or preempt controls to ensure
that this does not happen.
- FChE