On Feb 12, 2014, at 16:42, Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> Hello, Trond,
>
> In nfs4_destroy_session(), there is an rcu_dereference() that looks to
> leak the returned pointer out of an RCU read-side critical section.
> If the pointed-to object might have just now been created, this is a
> bug because xprt_destroy_backchannel() dereferences this pointer.
>
> So, does xprt_destroy_backchannel() exclude creation-side code? (If so,
> no bug -- but a comment might be good.)
>
> Thanx, Paul
>
> void nfs4_destroy_session(struct nfs4_session *session)
> {
> struct rpc_xprt *xprt;
> struct rpc_cred *cred;
>
> cred = nfs4_get_clid_cred(session->clp);
> nfs4_proc_destroy_session(session, cred);
> if (cred)
> put_rpccred(cred);
>
> rcu_read_lock();
> xprt = rcu_dereference(session->clp->cl_rpcclient->cl_xprt);
> rcu_read_unlock();
> dprintk("%s Destroy backchannel for xprt %p\n",
> __func__, xprt);
> xprt_destroy_backchannel(xprt, NFS41_BC_MIN_CALLBACKS);
> nfs4_destroy_session_slot_tables(session);
> kfree(session);
> }
>
Hi Paul,
nfs4_destroy_session() is only called when we’re tearing down the struct nfs_client that owns the cl_rppcclient, and the associated cl_xprt, so the code above should be safe, despite being ugly.
Is there a better annotation for use in the above kind of situation?
Cheers,
Trond
_________________________________
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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