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Subject: Re: [PATCH v7 3.2-rc2 9/30] uprobes: Background page replacement.
From: Peter Zijlstra <peterz@infradead.org>
In-Reply-To: <20111118110823.10512.74338.sendpatchset@srdronam.in.ibm.com>
References: <20111118110631.10512.73274.sendpatchset@srdronam.in.ibm.com>
	 <20111118110823.10512.74338.sendpatchset@srdronam.in.ibm.com>
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Date: Fri, 25 Nov 2011 15:29:24 +0100
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To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>, Linux-mm <linux-mm@kvack.org>, Ingo Molnar <mingo@elte.hu>, Andi Kleen <andi@firstfloor.org>, Christoph Hellwig <hch@infradead.org>, Steven Rostedt <rostedt@goodmis.org>, Roland McGrath <roland@hack.frob.com>, Thomas Gleixner <tglx@linutronix.de>, Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>, Arnaldo Carvalho de Melo <acme@infradead.org>, Anton Arapov <anton@redhat.com>, Ananth N Mavinakayanahalli <ananth@in.ibm.com>, Jim Keniston <jkenisto@linux.vnet.ibm.com>, Stephen Wilson <wilsons@start.ca>

On Fri, 2011-11-18 at 16:38 +0530, Srikar Dronamraju wrote:
> +       /* poke the new insn in, ASSUMES we don't cross page boundary */
> +       vaddr &= ~PAGE_MASK;
> +       memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz);

I still don't get why you don't simply write something like:

BUG_ON(vaddr + uprobe_opcode_size >= PAGE_SIZE);

That's as descriptive as the comment and actually does something if
someone got it wrong, instead of silently corrupting crap.

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