linux-kernel - Re: [PATCH v2 2.6.38-rc8-tip 5/20] 5: Uprobes: register/unregister probes.

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Message-ID: <20110318185314.GB24048@linux.vnet.ibm.com>
Date:	Sat, 19 Mar 2011 00:23:14 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2.6.38-rc8-tip 5/20] 5: Uprobes: register/unregister
 probes.

> > 
> > One of the install_uprobe could be failing because the process was
> > almost exiting, something like there was no mm->owner. Also lets
> > assume that the first few install_uprobes go thro and the last
> > install_uprobe fails. There could be breakpoint hits corresponding to
> > the already installed uprobes that get displayed. i.e all
> > breakpoint hits from the first install_uprobe to the time we detect a
> > failed a install_uprobe and revert all inserted breakpoints will be
> > shown as being captured.
> 
> I think you can gracefully deal with the exit case and simply ignore
> that one. But you cannot let arbitrary installs fail and still report
> success, that gives very weak and nearly useless semantics.

If there are more than one instance of a process running and if one
instance of a process has a probe thro ptrace, install_uprobe would fail
for that process with -EEXIST since we dont want to probe locations that
have breakpoints already. Should we then act similar to the exit case,
do we also deal gracefully?

-- 
Thanks and Regards
Srikar
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