linux-kernel - Re: [PATCH v8 3.2.0-rc5 1/9] uprobes: Install and remove breakpoints.

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Message-ID: <20120106110824.GD14946@linux.vnet.ibm.com>
Date:	Fri, 6 Jan 2012 16:38:24 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, 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 Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v8 3.2.0-rc5 1/9] uprobes: Install and remove
 breakpoints.

* Peter Zijlstra <peterz@...radead.org> [2012-01-06 11:57:41]:

> On Fri, 2012-01-06 at 11:44 +0530, Srikar Dronamraju wrote:
> >         - consumers for the uprobe is NULL, so mmap_uprobe will not
> >           insert new breakpoints which correspond to this uprobe until
> >           or unless another consumer gets added for the same probe.
> > 
> >         - If a new consumer gets added for this probe, we reuse the
> >           uprobe struct.
> 
> Ok, and when we install a new 'first' consumer we'll again try and
> install all breakpoints ignoring those that were already there?
> 

Yes, We install breakpoints as if its the first time a probe has been
requested to be installed, including setting the UPROBES_RUN_HANDLER
flag.

We do check if existing breakpoints are around during the actual
insertion, in which case install_breakpoint() will return -EEXIST.
However register assumes EEXIST to be non-fatal, and continues as if its
successful.

-- 
Thanks and Regards
Srikar

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