linux-kernel - Re: [tip:tracing/core] x86/tracing: comment need for atomic nop

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Date:	Sat, 12 Sep 2009 09:45:15 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	rostedt@...dmis.org, srostedt@...hat.com, tglx@...utronix.de
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:tracing/core] x86/tracing: comment need for atomic nop

* tip-bot for Steven Rostedt (srostedt@...hat.com) wrote:
> Commit-ID:  fc06b8520b3bf9aaeb2e27debe6719c215bd4916
> Gitweb:     http://git.kernel.org/tip/fc06b8520b3bf9aaeb2e27debe6719c215bd4916
> Author:     Steven Rostedt <srostedt@...hat.com>
> AuthorDate: Thu, 10 Sep 2009 17:22:44 -0400
> Committer:  Steven Rostedt <rostedt@...dmis.org>
> CommitDate: Thu, 10 Sep 2009 17:22:44 -0400
> 
> x86/tracing: comment need for atomic nop
> 
> The dynamic function tracer relys on the macro P6_NOP5 always being
> an atomic NOP. If for some reason it is changed to be two operations
> (like a nop2 nop3) it can faults within the kernel when the function
> tracer modifies the code.
> 
> This patch adds a comment to note that the P6_NOPs are expected to
> be atomic. This will hopefully prevent anyone from changing that.
> 
> Reported-by: Mathieu Desnoyer <mathieu.desnoyers@...ymtl.ca>

With an added "s" to my last name, that will be good.

Thanks !

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>

> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> 
> 
> ---
>  arch/x86/include/asm/nops.h |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/asm/nops.h b/arch/x86/include/asm/nops.h
> index ad2668e..6d8723a 100644
> --- a/arch/x86/include/asm/nops.h
> +++ b/arch/x86/include/asm/nops.h
> @@ -65,6 +65,8 @@
>     6: osp nopl 0x00(%eax,%eax,1)
>     7: nopl 0x00000000(%eax)
>     8: nopl 0x00000000(%eax,%eax,1)
> +   Note: All the above are assumed to be a single instruction.
> +	There is kernel code that depends on this.
>  */
>  #define P6_NOP1	GENERIC_NOP1
>  #define P6_NOP2	".byte 0x66,0x90\n"

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