Commit 0625c2dd authored Oct 17, 2013 by Chuck Lever Committed by Trond Myklebust Oct 28, 2013

NFS: Fix possible endless state recovery wait



In nfs4_wait_clnt_recover(), hold a reference to the clp being
waited on.  The state manager can reduce clp->cl_count to 1, in
which case the nfs_put_client() in nfs4_run_state_manager() can
free *clp before wait_on_bit() returns and allows
nfs4_wait_clnt_recover() to run again.

The behavior at that point is non-deterministic.  If the waited-on
bit still happens to be zero, wait_on_bit() will wake the waiter as
expected.  If the bit is set again (say, if the memory was poisoned
when freed) wait_on_bit() can leave the waiter asleep.

This is a narrow fix which ensures the safety of accessing *clp in
nfs4_wait_clnt_recover(), but does not address the continued use
of a possibly freed *clp after nfs4_wait_clnt_recover() returns
(see nfs_end_delegation_return(), for example).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

parent cd3fadec

fs/nfs/nfs4state.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -1255,14 +1255,16 @@ int nfs4_wait_clnt_recover(struct nfs_client *clp)

		might_sleep();

		atomic_inc(&clp->cl_count);
		res = wait_on_bit(&clp->cl_state, NFS4CLNT_MANAGER_RUNNING,
		nfs_wait_bit_killable, TASK_KILLABLE);
		if (res)
		return res;

		goto out;
		if (clp->cl_cons_state < 0)
		return clp->cl_cons_state;
		return 0;
		res = clp->cl_cons_state;
		out:
		nfs_put_client(clp);
		return res;
		}

		int nfs4_client_recover_expired_lease(struct nfs_client *clp)