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Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.
- From: Peter Zijlstra <peterz at infradead dot org>
- To: Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
- Cc: Ingo Molnar <mingo at elte dot hu>, Steven Rostedt <rostedt at goodmis dot org>, linux-mm at kvack dot org, Arnaldo Carvalho de Melo <acme at infradead dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Christoph Hellwig <hch at infradead dot org>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, Oleg Nesterov <oleg at redhat dot com>, Andrew Morton <akpm at linux-foundation dot org>, SystemTap <systemtap at sources dot redhat dot com>, Jim Keniston <jkenisto at linux dot vnet dot ibm dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Andi Kleen <andi at firstfloor dot org>, LKML <linux-kernel at vger dot kernel dot org>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>
- Date: Wed, 26 Jan 2011 11:10:56 +0100
- Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.
- References: <20101216095714.23751.52601.sendpatchset@localhost6.localdomain6> <20101216095817.23751.76989.sendpatchset@localhost6.localdomain6> <1295957745.28776.723.camel@laptop> <20110126074737.GA19725@linux.vnet.ibm.com>
On Wed, 2011-01-26 at 13:17 +0530, Srikar Dronamraju wrote:
> * Peter Zijlstra <peterz@infradead.org> [2011-01-25 13:15:45]:
>
> > > +
> > > + if (atomic_read(&uprobe->ref) == 1) {
> > > + synchronize_sched();
> > > + rb_erase(&uprobe->rb_node, &uprobes_tree);
> >
> > How is that safe without holding the treelock?
>
> Right,
> Something like this should be good enuf right?
>
> if (atomic_read(&uprobe->ref) == 1) {
> synchronize_sched();
> spin_lock_irqsave(&treelock, flags);
> rb_erase(&uprobe->rb_node, &uprobes_tree);
> spin_lock_irqrestore(&treelock, flags);
> iput(uprobe->inode);
> }
>
How is the atomic_read() not racy with a future increment, and what is
that synchronize_sched() thing for?