From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <peterz@infradead.org>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Anton Arapov <anton@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Roland McGrath <roland@hack.frob.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/7] ptrace: Partly fix set_task_blockstep()->update_debugctlmsr() logic
Date: Mon, 10 Sep 2012 18:57:17 +0200 [thread overview]
Message-ID: <20120910165717.GA17118@linutronix.de> (raw)
In-Reply-To: <20120903152609.GA9071@redhat.com>
* Oleg Nesterov | 2012-09-03 17:26:09 [+0200]:
>Afaics the usage of update_debugctlmsr() and TIF_BLOCKSTEP in
>step.c was always very wrong.
>
>1. update_debugctlmsr() was simply unneeded. The child sleeps
> TASK_TRACED, __switch_to_xtra(next_p => child) should notice
> TIF_BLOCKSTEP and set/clear DEBUGCTLMSR_BTF after resume if
> needed.
>
>2. It is wrong. The state of DEBUGCTLMSR_BTF bit in CPU register
> should always match the state of current's TIF_BLOCKSTEP bit.
>
>3. Even get_debugctlmsr() + update_debugctlmsr() itself does not
> look right. Irq can change other bits in MSR_IA32_DEBUGCTLMSR
> register or the caller can be preempted in between.
ptrace and uprobe are calling this function from process context. As
long as you have here get_cpu() instead of local_irq_disable() you should
be safe here.
The only user that is touching this bits in irq context is perf. perf
uses raw_local_irqsave() (raw_* most likely due to -RT). I have no idea
what you can against NMI unless not touching the register in NMI
context.
Sebastian
next prev parent reply other threads:[~2012-09-10 16:57 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-03 15:25 [PATCH 0/7] uprobes: single-step fixes Oleg Nesterov
2012-09-03 15:25 ` [PATCH 1/7] uprobes: Introduce arch_uprobe_enable/disable_step() Oleg Nesterov
2012-09-07 14:57 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 2/7] uprobes: x86: Implement x86 specific arch_uprobe_*_step Oleg Nesterov
2012-09-07 14:59 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 3/7] ptrace: Introduce set_task_blockstep() helper Oleg Nesterov
2012-09-07 15:00 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 4/7] ptrace: Partly fix set_task_blockstep()->update_debugctlmsr() logic Oleg Nesterov
2012-09-07 15:14 ` Srikar Dronamraju
2012-09-10 16:57 ` Sebastian Andrzej Siewior [this message]
2012-09-10 17:45 ` Peter Zijlstra
2012-09-10 17:27 ` Oleg Nesterov
2012-09-03 15:26 ` [PATCH 5/7] uprobes: Do not (ab)use TIF_SINGLESTEP/user_*_single_step() for single-stepping Oleg Nesterov
2012-09-07 15:11 ` Srikar Dronamraju
2012-09-07 15:50 ` Oleg Nesterov
2012-09-08 7:49 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 6/7] uprobes: Xol should send SIGTRAP if X86_EFLAGS_TF was set Oleg Nesterov
2012-09-12 12:08 ` Srikar Dronamraju
2012-09-12 14:45 ` Oleg Nesterov
2012-09-03 15:26 ` [PATCH 7/7] uprobes: Make arch_uprobe_task->saved_trap_nr "unsigned int" Oleg Nesterov
2012-09-12 12:27 ` Srikar Dronamraju
2012-09-08 17:06 ` [PATCH 0/7] uprobes: single-step fixes Oleg Nesterov
2012-09-12 12:33 ` Srikar Dronamraju
2012-09-08 17:06 ` [PATCH 8/7] uprobes: Fix arch_uprobe_disable_step() && UTASK_SSTEP_TRAPPED interaction Oleg Nesterov
2012-09-12 12:36 ` Srikar Dronamraju
2012-09-10 16:57 ` [PATCH 0/7] uprobes: single-step fixes Sebastian Andrzej Siewior
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