On Wed, Jan 30, 2008 at 04:37:49PM +0100, Andrea Arcangeli wrote:
> On Tue, Jan 29, 2008 at 06:29:10PM -0800, Christoph Lameter wrote:
> > +void mmu_notifier_release(struct mm_struct *mm)
> > +{
> > + struct mmu_notifier *mn;
> > + struct hlist_node *n, *t;
> > +
> > + if (unlikely(!hlist_empty(&mm->mmu_notifier.head))) {
> > + rcu_read_lock();
> > + hlist_for_each_entry_safe_rcu(mn, n, t,
> > + &mm->mmu_notifier.head, hlist) {
> > + hlist_del_rcu(&mn->hlist);
>
> This will race and kernel crash against mmu_notifier_register in
> SMP. You should resurrect the per-mmu_notifier_head lock in my last
> patch (except it can be converted from a rwlock_t to a regular
> spinlock_t) and drop the mmap_sem from
> mmu_notifier_register/unregister.
Agree.
That will also resolve the problem we discussed yesterday.
I want to unregister my mmu_notifier when a GRU segment is
unmapped. This would not necessarily be at task termination.
However, the mmap_sem is already held for write by the core
VM at the point I would call the unregister function.
Currently, there is no __mmu_notifier_unregister() defined.
Moving to a different lock solves the problem.
-- jack
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