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SubjectRe: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.
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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?


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