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From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will.deacon@arm.com>,
	"Jon Medhurst (Tixy)" <tixy@linaro.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Rabin Vincent <rabin@rab.in>, Ingo Molnar <mingo@redhat.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] ARM: ftrace: Ensure code modifications are synchronised across all cpus
Date: Mon, 10 Dec 2012 13:57:48 +0000	[thread overview]
Message-ID: <20121210135747.GK14363@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <1355144537.17101.155.camel@gandalf.local.home>

On Mon, Dec 10, 2012 at 08:02:17AM -0500, Steven Rostedt wrote:
> On Mon, 2012-12-10 at 10:04 +0000, Will Deacon wrote:
> > Yes, and I think if you do use two 16-bit nops, you can even get rid of all
> > the intermediate `sync' operations (I guess you might want one at the end if
> > you want the call to become visible at a particular point).
> 
> Wont work. We are replacing a 32bit call with a nop. That nop must also
> be 32bits, because we could eventually replace the nop(s) with a 32bit
> call.

... which, if it's misaligned to a 32-bit boundary, which can happen with
Thumb-2 code, will require the replacement to be done atomically; you will
need to use stop_machine() to ensure that other CPUs don't try to execute
the instruction mid-way through modification... as I have already
explained in my previous mails.

  parent reply	other threads:[~2012-12-10 13:58 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-12-06 18:11 [PATCH] ARM: ftrace: Ensure code modifications are synchronised across all cpus Jon Medhurst (Tixy)
2012-12-06 19:19 ` Steven Rostedt
2012-12-07  9:22   ` Jon Medhurst (Tixy)
2012-12-07 14:03     ` Steven Rostedt
2012-12-07 14:55       ` Jon Medhurst (Tixy)
2012-12-07 15:28         ` Steven Rostedt
2012-12-07 15:40           ` Jon Medhurst (Tixy)
2012-12-07 16:09             ` Steven Rostedt
2012-12-07 16:23           ` Russell King - ARM Linux
2012-12-07 16:36             ` Steven Rostedt
2012-12-07 16:45               ` Russell King - ARM Linux
2012-12-07 17:13                 ` Steven Rostedt
2012-12-07 17:45                   ` Jon Medhurst (Tixy)
2012-12-07 18:06                     ` Steven Rostedt
2012-12-07 18:17                       ` Steven Rostedt
2012-12-07 18:18                       ` Jon Medhurst (Tixy)
2012-12-10 10:04                     ` Will Deacon
2012-12-10 13:02                       ` Steven Rostedt
2012-12-10 13:33                         ` Will Deacon
2012-12-10 13:40                         ` Jamie Lokier
2012-12-10 14:56                           ` Will Deacon
2012-12-10 13:57                         ` Russell King - ARM Linux [this message]
2012-12-10 14:06                           ` Steven Rostedt
2012-12-10 14:07                             ` Russell King - ARM Linux
2012-12-10 14:46                               ` Steven Rostedt
2012-12-10 15:25                                 ` Russell King - ARM Linux
2012-12-10 16:31                                   ` Steven Rostedt
2012-12-10 16:45                       ` Jon Medhurst (Tixy)
2012-12-07 18:13                   ` Russell King - ARM Linux
2012-12-07 18:43                     ` Steven Rostedt
2012-12-07 19:02                       ` Will Deacon
2012-12-07 20:01                         ` Steven Rostedt
2012-12-10 11:04                         ` Jon Medhurst (Tixy)
2012-12-10 11:24                           ` Will Deacon
2012-12-10 14:02                             ` Steven Rostedt

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