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Re: [PATCH] Linux Kernel Markers
- From: "S. P. Prasanna" <prasanna at in dot ibm dot com>
- To: Alan Cox <alan at lxorguk dot ukuu dot org dot uk>
- Cc: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>, Martin Bligh <mbligh at google dot com>, Andrew Morton <akpm at osdl dot org>, "Frank Ch. Eigler" <fche at redhat dot com>, 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
- Date: Wed, 20 Sep 2006 06:38:52 +0530
- Subject: Re: [PATCH] Linux Kernel Markers
- References: <20060919081124.GA30394@elte.hu> <451008AC.firstname.lastname@example.org> <20060919154612.GU3951@redhat.com> <4510151B.email@example.com> <firstname.lastname@example.org> <45101DBA.email@example.com> <20060919063821.GB23836@in.ibm.com> <firstname.lastname@example.org> <20060919175405.GC26339@Krystal> <email@example.com>
- Reply-to: prasanna at in dot ibm dot com
On Wed, Sep 20, 2006 at 01:08:45AM +0100, Alan Cox wrote:
> Ar Maw, 2006-09-19 am 13:54 -0400, ysgrifennodd Mathieu Desnoyers:
> > Very good idea.. However, overwriting the second instruction with a jump could
> > be dangerous on preemptible and SMP kernels, because we never know if a thread
> > has an IP in any of its contexts that would return exactly at the middle of the
> > jump.
> No: on x86 it is the *same* case for all of these even writing an int3.
> One byte or a megabyte,
> You MUST ensure that every CPU executes a serializing instruction before
> it hits code that was modified by another processor. Otherwise you get
> CPU errata and the CPU produces results which vendors like to describe
> as "undefined".
Are you referring to Intel erratum "unsynchronized cross-modifying code"
- where it refers to the practice of modifying code on one processor
where another has prefetched the unmodified version of the code.
> Thus you have to serialize, and if you are serializing it really doesn't
> matter if you write a byte, a paragraph or a page.
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