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Subject: Re: [PATCH v5 3.1.0-rc4-tip 1/26]   uprobes: Auxillary routines to
 insert, find, delete uprobes
From: Peter Zijlstra <peterz@infradead.org>
To: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>, Ingo Molnar <mingo@elte.hu>,
        Steven Rostedt <rostedt@goodmis.org>, Linux-mm <linux-mm@kvack.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>, Hugh Dickins <hughd@google.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jonathan Corbet <corbet@lwn.net>, Thomas Gleixner <tglx@linutronix.de>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Roland McGrath <roland@hack.frob.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>
Date: Mon, 26 Sep 2011 13:18:38 +0200
In-Reply-To: <20110920154259.GA25610@stefanha-thinkpad.localdomain>
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On Tue, 2011-09-20 at 16:42 +0100, Stefan Hajnoczi wrote:
> On Tue, Sep 20, 2011 at 05:29:49PM +0530, Srikar Dronamraju wrote:
> > +static void delete_uprobe(struct uprobe *uprobe)
> > +{
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&uprobes_treelock, flags);
> > +	rb_erase(&uprobe->rb_node, &uprobes_tree);
> > +	spin_unlock_irqrestore(&uprobes_treelock, flags);
> > +	put_uprobe(uprobe);
> > +	iput(uprobe->inode);
> 
> Use-after-free when put_uprobe() kfrees() the uprobe?

I suspect the caller still has one, and this was the reference for being
part of the tree. But yes, that could do with a comment.

The comment near atomic_set() in __insert_uprobe() isn't too clear
either. /* get access + drop ref */, would naively seem +1 -1 = 0,
instead of +1 +1 = 2.