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Subject[PATCH 4.4 015/118] nfsd: Close race between nfsd4_release_lockowner and nfsd4_lock
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chuck Lever <chuck.lever@oracle.com>

commit 885848186fbc2d1d8fb6d2fdc2156638ae289a46 upstream.

nfsd4_release_lockowner finds a lock owner that has no lock state,
and drops cl_lock. Then release_lockowner picks up cl_lock and
unhashes the lock owner.

During the window where cl_lock is dropped, I don't see anything
preventing a concurrent nfsd4_lock from finding that same lock owner
and adding lock state to it.

Move release_lockowner() into nfsd4_release_lockowner and hang onto
the cl_lock until after the lock owner's state cannot be found
again.

Found by inspection, we don't currently have a reproducer.

Fixes: 2c41beb0e5cf ("nfsd: reduce cl_lock thrashing in ... ")
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/nfsd/nfs4state.c | 40 +++++++++++++++++-----------------------
1 file changed, 17 insertions(+), 23 deletions(-)

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1200,27 +1200,6 @@ free_ol_stateid_reaplist(struct list_hea
}
}

-static void release_lockowner(struct nfs4_lockowner *lo)
-{
- struct nfs4_client *clp = lo->lo_owner.so_client;
- struct nfs4_ol_stateid *stp;
- struct list_head reaplist;
-
- INIT_LIST_HEAD(&reaplist);
-
- spin_lock(&clp->cl_lock);
- unhash_lockowner_locked(lo);
- while (!list_empty(&lo->lo_owner.so_stateids)) {
- stp = list_first_entry(&lo->lo_owner.so_stateids,
- struct nfs4_ol_stateid, st_perstateowner);
- WARN_ON(!unhash_lock_stateid(stp));
- put_ol_stateid_locked(stp, &reaplist);
- }
- spin_unlock(&clp->cl_lock);
- free_ol_stateid_reaplist(&reaplist);
- nfs4_put_stateowner(&lo->lo_owner);
-}
-
static void release_open_stateid_locks(struct nfs4_ol_stateid *open_stp,
struct list_head *reaplist)
{
@@ -5952,6 +5931,7 @@ nfsd4_release_lockowner(struct svc_rqst
__be32 status;
struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
struct nfs4_client *clp;
+ LIST_HEAD (reaplist);

dprintk("nfsd4_release_lockowner clientid: (%08x/%08x):\n",
clid->cl_boot, clid->cl_id);
@@ -5982,9 +5962,23 @@ nfsd4_release_lockowner(struct svc_rqst
nfs4_get_stateowner(sop);
break;
}
+ if (!lo) {
+ spin_unlock(&clp->cl_lock);
+ return status;
+ }
+
+ unhash_lockowner_locked(lo);
+ while (!list_empty(&lo->lo_owner.so_stateids)) {
+ stp = list_first_entry(&lo->lo_owner.so_stateids,
+ struct nfs4_ol_stateid,
+ st_perstateowner);
+ WARN_ON(!unhash_lock_stateid(stp));
+ put_ol_stateid_locked(stp, &reaplist);
+ }
spin_unlock(&clp->cl_lock);
- if (lo)
- release_lockowner(lo);
+ free_ol_stateid_reaplist(&reaplist);
+ nfs4_put_stateowner(&lo->lo_owner);
+
return status;
}


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