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Re: [PATCH] Linux Kernel Markers
- From: Alan Cox <alan at lxorguk dot ukuu dot org dot uk>
- To: Helge Hafting <helge dot hafting at aitel dot hist dot no>
- Cc: prasanna at in dot ibm dot com, 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>, Mathieu Desnoyers <mathieu dot desnoyers at polymtl dot ca>, 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 11:30:26 +0100
- Subject: Re: [PATCH] Linux Kernel Markers
- References: <20060918234502.GA197@Krystal> <20060919081124.GA30394@elte.hu> <451008AC.6030006@google.com> <20060919154612.GU3951@redhat.com> <4510151B.5070304@google.com> <20060919093935.4ddcefc3.akpm@osdl.org> <45101DBA.7000901@google.com> <20060919063821.GB23836@in.ibm.com> <45110C6B.6010909@aitel.hist.no>
Ar Mer, 2006-09-20 am 11:39 +0200, ysgrifennodd Helge Hafting:
> Yes, 5 bytes is not an atomic write except on 64-bit. So a race is possible.
Untrue as well. Pentium and later have CMPXCHG8.
> How about this workaround:
> 1. Overwrite the start of the function with a hlt, which is atomic.
> 2. Write that 5-byte jump after the hlt.
> 3. Overwrite the hlt with nop so things will work
> 4. interrupt any cpus that got stuck on the hlt - or just wait for the
> timer.
CPU errata time again. You have to synchronize.
Alan