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From: Linus Torvalds <torvalds@linux-foundation.org>
To: mingo@kernel.org, hpa@zytor.com, eranian@google.com,
	linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl,
	torvalds@linux-foundation.org, fweisbec@gmail.com,
	akpm@linux-foundation.org, tglx@linutronix.de
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perf/core] perf/x86: Fix USER/KERNEL tagging of samples
Date: Fri, 6 Jul 2012 09:29:33 -0700
Message-ID: <CA+55aFxY7SqwSQWuRXSg+W=ftp9FtCT1MMEqMiCi1H279Fis-A@mail.gmail.com> (raw)
In-Reply-To: <tip-xxrt0a1zronm1sm36obwc2vy@git.kernel.org>

On Thu, Jul 5, 2012 at 11:20 PM, tip-bot for Peter Zijlstra
<a.p.zijlstra@chello.nl> wrote:
>
> Several perf interrupt handlers (PEBS,IBS,BTS) re-write regs->ip but
> do not update the segment registers. So use an regs->ip based test
> instead of an regs->cs/regs->flags based test.

Christ, people, YOU CANNOT DO THIS!

It is never *ever* valid to test the IP to see if you're in kernel
space or user space. People can do various odd segments etc, the IP is
totally meaningless.

If the perf handlers fake the IP information, they had better fake the
CS/eflags information too. Because it is *wrong* to look at IP. Don't
do it.

                Linus

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-06  6:20 tip-bot for Peter Zijlstra
2012-07-06 16:29 ` Linus Torvalds [this message]
2012-07-06 18:12   ` Peter Zijlstra
2012-07-06 18:16     ` Linus Torvalds
2012-07-06 18:34       ` Linus Torvalds
2012-07-06 20:48         ` Peter Zijlstra
2012-07-06 20:59           ` Linus Torvalds
2012-07-09 11:23         ` Peter Zijlstra
2012-07-09 17:55           ` Linus Torvalds
2012-07-10  9:02             ` Peter Zijlstra
2012-07-10  9:48               ` Ingo Molnar
2012-07-10  9:50               ` Peter Zijlstra
2012-07-10  9:52                 ` Peter Zijlstra
2012-07-10  9:55                 ` Ingo Molnar
2012-07-31 17:57               ` [tip:perf/urgent] perf/x86: Fix USER/ KERNEL tagging of samples properly tip-bot for Peter Zijlstra
2012-07-09 18:41           ` [tip:perf/core] perf/x86: Fix USER/KERNEL tagging of samples Ingo Molnar
2012-07-10  7:54             ` Peter Zijlstra
2012-07-10  8:02               ` Ingo Molnar
2012-07-10  8:21               ` Ingo Molnar
2012-07-10  8:52                 ` Peter Zijlstra
2012-07-10  9:48                   ` Ingo Molnar
2012-07-31 18:11                     ` H. Peter Anvin

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