From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH v2 0/7] Allow disabling HW_BREAKPOINTS, PERF_EVENTS,
	INSTRUCTION_DECODER, IRQ_WORK, ANON_INODES
Date: Mon, 10 Mar 2014 15:50:30 +0100
Message-ID: <20140310145030.GD21735@redhat.com>
References: <cover.1394418994.git.josh@joshtriplett.org>
	<20140310074354.GA4890@gmail.com>
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Cc: kvm@vger.kernel.org, Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	David Herrmann <dh.herrmann@gmail.com>,
	Stephane Eranian <eranian@google.com>,
	Paul Gortmaker <paul.gortmaker@windriver.com>,
	Paul Mackerras <paulus@samba.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andi Kleen <ak@linux.intel.com>, x86@kernel.org,
	Ingo Molnar <mingo@redhat.com>, oprofile-list@lists.sf.net,
	Mel Gorman <mgorman@suse.de>,
	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
	Borislav Petkov <bp@suse.de>, Dave Young <dyoung@redhat.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>, Gleb Natapov <gleb@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Steven Rostedt <rostedt@goodmis.org>, Bin Gao <bin.gao@intel.com>,
	Matt Fleming <matt.fleming@intel.com>,
	Jacob Shin <jacob.shin@amd.com>, linux-kernel@vger.kernel.
To: Ingo Molnar <mingo@kernel.org>
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On 03/10, Ingo Molnar wrote:
>
> So my main problem with those patches was that if HW_BREAKPOINTS is
> disabled then GDB 'hbreak' isn't simply disabled but fails in various
> non-obvious ways,

but the kernel should return an error. And this can happen anyway, say,
reserve_bp_slot() can fail because all slots are already used by perf.

And iirc, gdb always switches to the single-stepping if hbreak fails.

Oleg.


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