Messages in this thread | | | Date | Tue, 31 Oct 2006 12:15:32 +0900 | From | "Akinobu Mita" <> | Subject | Re: [PATCH 2/2] auth_gss: unregister gss_domain when unloading module |
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2006/10/31, Trond Myklebust <Trond.Myklebust@netapp.com>: > On Mon, 2006-10-30 at 23:54 +0900, Akinobu Mita wrote: > > On Sun, Oct 29, 2006 at 03:15:59PM -0500, Trond Myklebust wrote: > > > > > > +void svcauth_gss_unregister_pseudoflavor(char *name) > > > > +{ > > > > + struct auth_domain *dom; > > > > + > > > > + dom = auth_domain_find(name); > > > > + if (dom) { > > > > + auth_domain_put(dom); > > > > + auth_domain_put(dom); > > > > + } > > > > +} > > > > > > Strictly speaking, if you want to be smp-safe, you probably need > > > something like the following: > > > > > > dom = auth_domain_find(name); > > > if (dom) { > > > spin_lock(&auth_domain_lock); > > > if (!hlist_unhashed(dom->hash)) { > > > hlist_del_init(dom->hash); > > > spin_unlock(&auth_domain_lock); > > > auth_domain_put(dom); > > > } else > > > spin_unlock(&auth_domain_lock); > > > auth_domain_put(dom); > > > } > > > > > > and then add a test for hlist_unhashed into auth_domain_put(). If not, > > > some other processor could race you inside > > > svcauth_gss_unregister_pseudoflavor. > > > > But auth_domain_table is protected by auth_domain_lock while we are > > using auth_domain_put()/auth_domain_lookup()/auth_domain_find(). > > So I think there is not big difference. > > No. The auth_domain_lock was released after the call to > auth_domain_find(), and thus there is no guarantee that the entry is > still referenced when you get round to that second call to > auth_domain_put(). Testing for hlist_unhashed() and then removing the > entry from the lookup table while under the spin lock fixes this > problem: it ensures that you only call auth_domain_put() once if some > other process has raced you. >
Thanks, I understand it.
But I noticed that even if we have this kind of smp-safe code, there is no guarantee that 2nd auth_domain_put() in svcauth_gss_unregister_pseudoflavor() is the last reference of this gss_domain.
So it is possible to happen invalid dereference by real last user of this gss_domain after unloading module. If this is not wrong, Is it neccesary to have try_get_module()/put_module() somewhere to prevent this? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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