linux-kernel - Re: [PATCH v7 3.2-rc2 9/30] uprobes: Background page replacement.

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Message-ID: <1322231365.2535.6.camel@laptop>
Date:	Fri, 25 Nov 2011 15:29:24 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...k.frob.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Stephen Wilson <wilsons@...rt.ca>
Subject: Re: [PATCH v7 3.2-rc2 9/30] uprobes: Background page replacement.

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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